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.

In your review of the new iPhone 3GS, you said that AT&T had changed its upgrade policy so some buyers of the previous model could get the new-customer price earlier than planned. Can you explain this in more detail?

Almost all cellphones in the U.S. are subsidized by the carriers to bring down prices. Typically, existing customers—who have already benefited from a subsidy—can’t upgrade at the lower new-customer price (in this case $199) until they reach a point in their contracts where this subsidy has been recovered. These dates vary, based on a formula that takes into account things like the customer’s monthly spending rate.

When some early adopters of the 2008 iPhone model, the 3G, discovered they wouldn’t immediately qualify for this $199 “standard upgrade” price—the same as the new-customer price—they got angry. So AT&T made a concession, but only a partial one. It declared that any customer who had been told he or she couldn’t get the $199 price until sometime in July, August or September of 2009 would in fact now be able to qualify for that lower price starting on the first day of availability.

This concession doesn’t apply at all to owners of the original 2007 iPhone, or even every owner of the 2008 3G model. And it isn’t based on when you bought your 3G, but when the system told you that you could buy the new model at the “standard” upgrade price of $199. You can check the price AT&T or Apple will charge you for an upgrade by going to www.att.com/iPhone and clicking on “Check upgrade eligibility.”

I’ve recently heard that the new Palm Pre smart phone is unable to import data from the old Palm Desktop program. In other words, if you have Palm Desktop filled with data from a previous Palm model, you’ll be unable to get that data into your new Palm Pre. Is this true?

No. While the Pre isn’t designed to repeatedly sync with the old Palm Desktop software, Palm does offer a program, for Windows and Mac, that will perform a one-time import of your old data from Palm Desktop. It can also do a one-time import of data from certain other desktop programs as well, including Microsoft Outlook on Windows, and iCal and Address Book on the Mac. This program will help you move your data to one of the online services, such as Google, with which the Pre is designed to sync continuously. The software is called the Palm Data Transfer Assistant and is free at http://bit.ly/3lIaZ.

I am contemplating purchasing the 17” MacBook Pro rather than the 13” or 15” models because the antiglare matte screen is offered only with the 17”. How bad is the glare on the smaller screens and how cumbersome do you find the larger 17” MacBook Pro?

For a laptop of its size, the 17” MacBook Pro is remarkably thin and light. But I did find it cumbersome to use in coach seats on airplanes and to cram into small briefcases. As for the glossy screens, which are now the most common option on many laptops, they bothered me at first, but I don’t notice the glare now. However, both of these are personal issues. So my suggestion is to go to a store and see for yourself.

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

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.

In last week’s Mailbox, you said that Windows XP machines can slow down over time unless you do “a lot of techie maintenance.” What did you mean? I regularly defragment the hard disk, tweak the registry, and clean out temporary files, but my PC is still slow.

All of these things are helpful, though I don’t recommend that nontechie users “tweak” the Windows registry, which contains vital program information that can mistakenly be removed or altered if you don’t know what you’re doing. Another speed-enhancing tactic is to use a program like Startup Cop Pro (snipurl.com/b4v91) to prevent unneeded programs from running at startup, and one like PC Decrapifier (pcdecrapifier.com) to clean out craplets — unwanted pre-installed programs.

However, what I had in mind when I wrote that was something more drastic, something a number of techies I know do annually: a complete replacement of Windows. This involves first backing up all your files, and then performing what’s called a “clean install” of Windows XP that wipes out everything on the PC and starts fresh. You then would copy back all your data files and re-install your programs.

This can make the computer feel like new, but the problem is that it can be tricky and tedious for nontechie users. Depending on the source of the copy of Windows XP you are using for the clean install, you may have to locate and re-install drivers for peripheral hardware and for hardware features of your particular make and model of PC. You may run into licensing and activation issues with your re-installed programs. And you may have to download numerous patches and upgrades for Windows itself and for your programs.

I am considering buying one of the new MacBook Pro 15″ laptops. What do you think of the keyboard on this laptop? Is it easy to type on compared to other laptop keyboards? What do you think of the shiny screen?

Because keyboard and screen preferences vary from person to person, I strongly urge all laptop shoppers to try out models they are considering before buying, even if only for a few minutes at a retail store. Having said that, I find the MacBook Pro keyboard to be very comfortable and easy to use, with good key spacing and feel. I personally prefer matte screens to glossy ones, but own laptops with both types and find the glossy ones acceptable, if not optimal.

I use the Windows Mail program that came with Vista on my computer. You say Windows 7 won’t come with that program. Is there something similar that can be installed?

Microsoft will encourage people to download a similar free program called Windows Live Mail, which is closely tied to its Live online service. Or, you could switch to a competing email program, or rely on Web-based email.

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.

Do you still recommend the Dell XPS One all-in-one computer that you favorably reviewed last December? I am not a techie at all but need to replace my 5-year-old Dell and was interested in an all-in-one.

Yes. In fact, I now own two of these Dell XPS Ones and use them as my Vista desktop computers, at home and in the office. I still believe, as I wrote in my review, that this Dell’s hardware is superior to that of the competing Apple iMac, though the Vista operating system is inferior to Apple’s. And the base XPS One now costs the same as the base iMac — $1,199 — instead of $300 more, as it did last year. So, if you want the Windows operating system, and like the look and convenience of an all-in-one desktop, I still favor the XPS One. You can find my review at tinyurl.com/2xw 6mv.

Will Apple’s new MacBooks and MacBook Pros run Windows directly without an intervening “virtual machine” program like Parallels or Fusion?

Yes. All Apple Macs running the current Leopard operating system, including the new laptops, come with the ability to directly run Windows XP or Vista. Using Apple’s built-in “Boot Camp” feature, you can start up the computer in Windows, instead of the Mac’s own operating system, which turns the Mac into a pure Windows machine, with no trace of the Mac operating system running. The upsides of this approach are maximum Windows speed, and compatibility with the most graphics-intensive Windows programs, including games. Note that, to run Windows on a Mac, you must obtain and install a fresh, boxed, full version of XP or Vista. Apple doesn’t supply Windows.

I have a Yahoo email account, and wonder if Yahoo allows receipt and storage of email directly via a computer email program, such as Outlook, or is it all Web storage? Can you do both?

Yes. Yahoo offers a “Plus” option, for $20 a year, that permits users to receive and store their Yahoo email using a locally installed, instead of Web-based, email program. This approach does work with Microsoft Office, as well as many other local email programs. And you can still use Yahoo’s Web-based email interface at the same time. The Plus option also includes other benefits, including the elimination of ads and a doubling of the size limit on individual messages, to 20 megabytes.

• 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.