A: Windows programs cannot be “converted” to run directly in the Mac operating system, which is called Snow Leopard. But, if you use virtualization software like Parallels or VMware fusion, and install Windows, then a Windows program like Microsoft Outlook can run simultaneously with your Mac programs. Technically, you are running it in Windows, but the two operating systems are active at the same time. With both of these virtualization products, you can even hide the entire Windows desktop, so that the Windows program you are running simply occupies a window on your Mac like any Mac program does. You don’t even notice that Windows is running.

In the case of files you created in Windows, the situation is even simpler. Most of the common types of files consumers use—including Microsoft Office documents, MP3 music files, MP4 video files, JPG picture files, text files, Adobe PDF files, and others—can be run in native Macintosh programs without conversion and without the need to run Windows programs. So you can just copy them to the Mac side and use them in Mac programs like iPhoto, iTunes, or the native Mac version of Microsoft Office, which uses the same file formats as the Windows version.

If you have an unusual or proprietary Windows file for which there isn’t an equivalent program on the Mac, you would run it in a Windows program, as described above.

If I am planning to upgrade a Windows XP machine to Windows 7, can I buy the upgrade copy of 7 or must I buy the full version?

A: According to Microsoft’s Web site, XP is one of the older versions of Windows upon which you can indeed indeed use the less expensive upgrade versions of Windows 7. The company’s online store says: “All editions of Windows XP and Windows Vista qualify you to upgrade. So, if you’re running either on your PC today, buy a package labeled ‘Upgrade’.”

I’ve been holding out (for what feels like forever) on purchasing a Netbook because I read that Apple was coming out with one. Can you tell me anything about when they might really begin selling them?

A: Apple executives have said repeatedly and emphatically that they don’t plan to offer a netbook, which is essentially a cheap, small laptop. Instead, Apple is widely believed to be working on a small slate or tablet device that would be controlled via a fingertip touch screen. This would be sort of like a larger iPhone or iPod Touch. The company hasn’t confirmed that such a product is in the works, but many analysts and Apple bloggers predict it will debut early next year.

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. This week my mailbox contained questions about external modems for a MacBook, resizing photos for email, and using the forthcoming iPhone in Europe.

In your laptop buying guide, you mentioned that the MacBook from Apple lacks both an internal cellphone modem and an external slot in which to insert one. Is there a way to hook up a cellphone modem via a USB port?

Yes, several cellphone carriers offer external modems that plug into USB ports. I haven’t tested these, but have no reason to doubt that they work. However, if you are buying a MacBook, make sure any such modem you buy is Mac-compatible. Both Verizon and Sprint carry a Novatel model that plugs into a USB port and is listed as being compatible with the Mac.

When I email pictures to my sister, she has to scroll up, down, and across to see the whole thing. What can I do to my computer or to hers?

You can make the picture smaller before emailing it. Both Windows and Macintosh computers offer you the option of shrinking the size of photos you email. For instance, in the My Pictures folder in Windows XP, if you select a photo and then choose “Email this file” from the menu at the left, you will be asked if you want to make the picture smaller. On the Mac, in the built-in iPhoto program, when you select a photo and click on the Email icon at the bottom, you are offered a choice of sizes for the picture.

Will the forthcoming Apple iPhone be usable in Europe with a SIM card, and will it be based on a Palm platform or a Microsoft one?

Nothing about any future product can be certain until it is released, but Apple officials have said that the iPhone will be usable in Europe if you insert into it a SIM card from a European carrier. However, it won’t have one of its touted features, “visual voicemail,” which depends upon AT&T, the iPhone’s U.S. carrier.

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Because of the volume of e-mail I receive, I can’t routinely answer individual questions by e-mail, or consult on individual problems or purchasing decisions. I read all questions I receive and select three each week to answer in the column.

Write to Walter S. Mossberg at mossberg@wsj.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. This week my mailbox contained questions about switching between software provided by camera companies, Web-based tax-preparation software and scheduling antispyware sweeps.

If you have a question, send it to me at mossberg@wsj.com, and I may select it to be answered here in Mossberg’s Mailbox.

I have been using Olympus digital cameras for years, so I have a library of Olympus digital photos using Olympus software. If I were to switch to a Canon camera, how easy is it to also switch software? Is there an easy way to transfer the Olympus photos into the Canon software?

Unless you are doing something unusual, all your photos from both cameras should be in the standard format called “jpg” and I assume either company’s software can handle all of them. However, I don’t recommend using the software supplied by camera makers. They may be fine at making cameras, but, with the exception of Kodak, they usually create lousy software. Instead, I suggest getting a good, general photo-organizing program, and making that the center for managing your pictures — whatever camera you use.

Every Macintosh computer comes with a superb program called iPhoto for organizing, sharing and editing photos. Windows computers don’t come with anything as good, but you can download a free program called Picasa from Google, at picasa.com. Or, you can download Kodak’s very nice EasyShare software, at Kodak.com. It’s free, comes in versions for both Windows and Mac, and doesn’t require a Kodak camera or printer to use. Paid software that also does the trick on Windows includes ACDSee, at acdsystems.com; and Corel Photo Album, at corel.com.

In 2002, you advised against using Web-based tax-preparation software, writing, “Your tax data are highly sensitive and confidential, and I think the Web is just too susceptible to hackers and crooks to make it a fitting repository for such information.” Do you continue to have these concerns?

Yes. If anything, the incidence of identity theft and other security problems on the Web have grown worse since 2002. I am not criticizing the tax-preparation companies, which I assume have good security. And I am not advising people against normal e-commerce, or the use of credit cards online. But I would be personally loath to put the broad and deep financial information required for a tax filing on a server controlled by someone else and connected to the Internet. I would instead download or buy traditional tax-preparation software, which keeps your data on your own hard disk.

I have the Spy Sweeper antispyware software that you recommend, and am wondering how often you suggest scheduling it to automatically scan my computer for software. I was thinking once a month.

Once a month isn’t good enough if you are an active Internet user, or your computer is on a broadband connection and stays on, and connected, all the time. I run both spyware and virus scans nightly on my Windows computers, and I advise all Windows broadband users to do so. There’s no downside, if your computer is on all the time anyway. I also advise setting the software to run in the background, guarding your PC against new intrusions.

Write to Walter S. Mossberg at mossberg@wsj.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. This week my mailbox contained questions about Internet security fears, red-eye elimination in photos and software availability for Macs.

If you have a question, send it to me at mossberg@wsj.com, and I may select it to be answered here in Mossberg’s Mailbox.

Are there any possible security dangers when a DSL modem is left on while the computer is turned off?

No, as long as it’s the only computer connected to the modem. The modem only fetches data from the Internet when a computer program, like a Web browser or email software, requests it to do so. If the computer is off, no such requests can be made, so no data, safe or unsafe, is being received. Similarly, if the computer is on but the modem is off, the computer isn’t connected to the Internet, and can’t receive any data, normal or malicious.

However, I feel compelled to note that, if you allow your Internet usage to be totally ruled by security fears, you may miss out on a lot. One of the great benefits of always-on broadband services like DSL is that your email flows in continuously; upgrades (including security upgrades) can be downloaded automatically, day or night; and you can take advantage of remote backup and file-synchronization services that work in the middle of the night.

I have a new Sony camera and need help editing my photos to eliminate red eye. I have small grandchildren who always have red eyes in my pictures. What software can I use to get rid of it?

Almost every photo software program I have tested has a red-eye elimination feature, and most are adequate. You just have to get the hang of it. If you have a Windows PC, try Google’s free Picasa program, or Adobe Photoshop Elements. On a Mac, you can use the built-in iPhoto software, or the Mac version of Photoshop Elements. You could also use a professional program like Photoshop, though that might be overkill.

I am thinking seriously that my next computer purchase will be an Apple. My question is: How prolific is the software that is written for Macs? I’m thinking of financial software like Quicken, but also the basic Office suite of products.

There are Mac versions of both Quicken and Microsoft Office. The latter can directly read and write to the same file formats as its Windows counterpart; the former cannot. Apple claims there are now thousands of software programs that run on the current Macs. So is there is a decent selection of software for general consumers.

However, there is vastly more software available for Windows, especially in certain categories like games, business software, databases and niche products for specific professions and hobbies. If you are likely to be satisfied with the main types of software — like office programs, Web browsers, email programs and multimedia players — you’ll be fine with the Mac. But if you are interested in any of these other categories, or in generally having the greatest selection, stick with Windows.

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Because of the volume of e-mail I receive, I can’t routinely answer individual questions by e-mail, or consult on individual problems or purchasing decisions. I read all questions I receive and select three each week to answer in the column.

Write to Walter S. Mossberg at mossberg@wsj.com