I have a vision problem and can barely read low-contrast print, even the light colors on your Web site. Any ideas for how I and others can solve this problem? I use a Mac and the Firefox Web browser.

A: If your Mac is running the Leopard or Snow Leopard operating systems, you can use an onscreen slider control or keyboard commands to enhance the contrast. You can even switch the display to white-on-black, which really boosts the effect. This works system-wide. These settings are found in System Preferences, under the Universal Access preference, in the tab called “Seeing,” in the section called “Display.”

The new Windows 7 also has a similar feature that applies a “high contrast theme” when you press a certain key combination. It can be enabled or disabled in the Control Panel, under Ease of Access. You click on “Ease of Access Center,” and then “Make the computer easier to see.”

Where can I download the Windows 7 Home Premium upgrade edition for my Vista Home Premium computer?

A: Windows 7 can be downloaded at http://store.microsoft.com/home.aspx. And, after you’ve installed it, you can upgrade to higher versions anytime, if you like, for a fee. This is called the Windows Anytime Upgrade, and is explained at this site: http://bit.ly/VrV58.

Do you know if the new Windows 7 Home Premium will be offered at less than the retail price of $120 to current Vista PC owners who wish to upgrade?

A: That $120 price is the upgrade price for Vista owners moving to Windows 7 Home Premium, though of course some retailers might discount it. The “full,” or non-upgrade, edition of Home Premium lists for $200. Microsoft did run a sale on Windows 7 pre-orders earlier this year, but that’s over.

You can also get a Windows 7 upgrade from participating PC makers free, or for a nominal fee, if you buy a new PC equipped with Vista before the end of January, 2010, or bought one after June 26, 2009. For the latter offer, consult: http://bit.ly/rjAz4.

You can find Mossberg’s Mailbox, and my other columns, online, free, at the All Things Digital web site, http://walt.allthingsd.com.

Corrections & Amplifications

An earlier version of this column erroneously stated that Windows 7 had to be purchased on a disk.

There are lots of reliable online sellers of laptops, and online buying is fine, provided you have somehow handled the machine and are familiar enough with it to be sure it’s the one you (or, in this case, your lucky wife) will be happy owning. In the case of Apple, a company whose products are rarely deeply discounted by third-party sellers, it often makes sense for online buyers to use the company’s own online store, at store.apple.com. I have found Apple’s online store to be easy to use, secure and reliable. And you get some minor benefits at the physical Apple stores if you buy directly from Apple.

However, other major online sellers with equally good reputations also carry Macs, and some do shave the prices. One good example I have used happily is amazon.com, which carries the latest MacBook Pros at discounts ranging from $5 to over $100, depending on model.

How can I set parental controls in Firefox?

The Firefox Web browser doesn’t have built-in parental controls. Its maker, Mozilla, notes that version 3.0 or later of the browser does support some of the parental-control features included in Windows Vista. But if you don’t have Vista, or want different controls, there are some add-ons for Firefox that provide these.

Among the ones Mozilla suggests using are Glubble for Families, and ProCon Latte. More information is at: support.mozilla.com/en-US/kb/Parental+controls.

Here are a few questions about computers I’ve received recently from people like you, and my answers. I have edited and restated the questions a bit, for readability.

I switched from PC to Mac a year ago, but now I am thinking of adding a Windows laptop. If I do, what kind of compatibility problem would I have? I would be using the laptop mostly to write, to send/receive email and to Web browse.

In the old days, there were compatibility problems, but most of those have gone away. Based on your simple predicted usage, I’d say that you should be fine. For instance, both Macs and PCs can interchangeably open and edit all of the major file types — JPG pictures, MP3 music, Microsoft Office documents, Adobe PDF files, etc. Email and instant messages can, of course, be exchanged between the two platforms, even if you are using different programs. And Macs understand Windows file extensions. Also, you can use both platforms simultaneously on the same home network to access the Internet.

In some cases, you might need different programs to open the same files on the two platforms. But even that obstacle has greatly diminished. For instance, programs like the Firefox and Safari Web browsers, Adobe Reader, iTunes, Microsoft Office, Google Earth, Picasa, Photoshop and many others come in native versions for both platforms that can handle the same files. And, of course, Web-based programs like Gmail and Yahoo Mail work on both. Sometimes, the same programs have different features and user interfaces on Windows and Macs, but I haven’t found these differences hard to master.

The biggest problems for average users are Quicken, whose Mac version is inferior and incompatible; Internet Explorer, which is no longer made for the Mac; and Microsoft Outlook, which is replaced on the Mac by a program called Entourage that is similar but uses a different file format. And networking can be tricky. In general, the Mac does a better job of seeing Windows PCs on a network than Windows does of seeing Macs.

I use Outlook Express for my email, and I store a lot of mail in local folders. Is there a simple way to back these up? If I buy a new computer, can they be transferred?

Yes. There are two methods. One is a manual method, which Microsoft explains in a detailed document at this Web site: support.microsoft.com/kb/270670.

The other, quicker, method is to obtain one of several utility programs that can back up your Outlook Express data and, in some cases, allow you to transfer it to another PC. I haven’t tested these in years, and thus can’t recommend one over another. But one example is a free program called Outlook Express Backup, which can be found at genie-soft.com/products/oeb. Another is a $40 program called Outlook Express Backup Wizard, which can be found at: outlook-express-backup.com.

Do you know of an iPhone GPS application that speaks directions? It would make the iPhone similar to a TomTom or Garvin GPS unit.

A: No, but Apple recently announced that, under its new 3.0 operating system for the iPhone, such programs will be possible. Several companies are believed to be working on them, and I expect them to be available later in the year. The reason none exist yet is partly legal, having to do with the licensing of the underlying maps.

• You can find Mossberg’s Mailbox, and my other columns, online free of charge at the new All Things Digital Web site, http://walt.allthingsd.com.

I am a Palm Treo user and would like to get an iPhone for the apps. But I have tried the virtual keyboard on the iPhone in the store and hate it. Is there a stylus you can use for better accuracy, or some software trick?

I don’t know if they improve accuracy, but there are several stylus brands made for the iPhone and iPod Touch. They are aimed at making typing easier, especially if you have long nails or are wearing gloves. One example is the Pogo, a $15 iPhone stylus from a company called Ten One Design, at tenonedesign.com.

In addition, there are several iPhone apps that attempt to help typing accuracy by allowing you to compose emails, text messages and Twitter posts using a wide, landscape keyboard rather than the narrower standard keyboard. You type your message in these apps, and then the app sends them to the iPhone’s email program for transmission. One that I have used is called TouchType. It works with email and Twitter, and costs 99 cents.

Another interesting solution is a free app called ShapeWriter, which lets you type by sliding your finger along a keyboard to connect the letters in words. You never have to lift your finger until you are done with a whole word. Messages you compose in ShapeWriter can be saved as notes or shipped to the email program for sending.

Finally, I should note two things about typing on an iPhone. First, it’s difficult to know if you’ll be comfortable with it from just a few minutes in a store, because it usually takes a few days to master. Second, some people won’t ever find it acceptable, and these folks should choose a phone that has a physical keyboard.

In your review of the new version of the Safari Web browser, you said some Web sites were publishing methods for undoing some of the changes in it that you criticized. Can you explain how I can do that?

There are two methods for changing Safari 4 so it looks and works more like the previous versions, while retaining its faster speed. One method involves typing techie commands into the computer. But, for mainstream users, I recommend another: downloading a new free utility called Safari 4 Buddy. It’s available at swoon.net/site/software.html.

Safari 4 Buddy allows you to just check off buttons that can change the placement of tabs in Safari 4 so they’re under the toolbars, rather than at the top of the screen, and restore the blue page-loading progress bar that Apple killed. It also permits users to change other settings Apple omitted from the browser’s Preferences menus. I have tested it and it works.

However, this utility works only on the Mac version of Safari 4. I don’t know of any way to make these changes in the Windows version. Also, there’s no guarantee that Apple won’t make future modifications to the browser that might reverse any customizations Safari 4 Buddy makes.

• You can find Mossberg’s Mailbox, and my other columns, online free of charge at the new All Things Digital Web site, http://walt.allthingsd.com.

I need some help sending videos to others. It seems that every video I try to send in various ways is always too large. I’ve tried to use a program that works with Outlook to compress the email attachment, but it’s always still too large. Is there a solution other than uploading them onto YouTube or something similar?

I suggest you try one of the services that specifically exist to transmit files that are too large for email. They typically work by having you upload the files to their servers, which, unlike YouTube, don’t expose them to the world. Seconds after you upload these files, your recipients receive an email that includes a specific link to the file you uploaded. The email is small because it includes only the link, not the file itself. The recipient clicks on the link, and the file is downloaded to his or her computer.

The service I use for this is called YouSendIt, and can be accessed at yousendit.com. It works in all the major Web browsers, and on both Windows and Macintosh computers. The company has a free plan that covers files of up to 100 megabytes in size, and allows each file to be downloaded up to 100 times, or up to a gigabyte of total downloads each month. For $10 a month, you get a maximum file size of two gigabytes, 500 downloads per file, and a monthly maximum limit of 40 gigabytes.

In my experience, YouSendIt works well. It can be used directly from within a browser, or via a small program called YouSendIt Express, that lives on your computer and handles large files faster than the browser version does. YouSendIt also offers an Outlook plug-in that can automatically route large downloads via the service rather than through regular email, though I haven’t tested this plug-in.

Our daughter is heading off to college this fall. She will be an art/graphic-design major, and the school recommended that she buy an Apple MacBook. I’m not sure if she should get what the college calls the “midlevel MacBook” or the “advanced MacBook.” The only differences are a slightly faster processor, a hard disk that is 40 gigabytes larger, and a “SuperDrive” for CDs and DVDs rather than a “Combo” drive. The price difference is $90. Which should we buy?

Either machine would be fine, and a lot depends on your budget, since college itself is of course very expensive. But I think, in this case, the extra $90 would be worth paying. This has nothing to do with the processor speed, which she probably wouldn’t even notice. But, if she is going to be creating a lot of graphics files, which can be large, the extra hard-disk space could be important.

The same goes for the CD/DVD drive options. The “SuperDrive” is Apple’s term for a drive that can create both DVDs and CDs, while the “Combo” drive can create only CDs. (Both drives can play both types of disks.) For someone who is producing large files, the ability to create DVDs can be handy, since DVDs have much higher capacities than CDs.

My laptop has been infected by rogue viruses, posing as antispyware programs, that I can’t get rid of. When I go on Google, I find a number of sites that claim to offer free software that will get rid of them, but I am reluctant to download anything onto my machine from a source that I am not sure of. What’s a reliable program that will do that job?

I would immediately buy a genuine, legitimate commercial antispyware program, install it and run it. The best ones I know of are Spyware Doctor by PC Tools, at pctools.com, and Spy Sweeper from Webroot, at Webroot.com. Each costs $30, but that price can save you a lot of heartache.

You can find Mossberg’s Mailbox, and my other columns, online, free, at the new All Things Digital Web site, http://walt.allthingsd.com.