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 in the market for a new HDTV and the newspaper ads are using terminology that I’m unfamiliar with. Do TVs rated at “720p” provide the same quality picture as those rated at “1080p”?

Technically, the answer is no, but it may not matter. The 1080p resolution is certainly higher, but almost nobody can tell the difference between the same material shown in the two resolutions on TV screens up to around 50″ in size and at the typical distances from which people watch those screens. Not only that, but most sources of video content, with the exception of Blu-ray discs, can’t even fully utilize 1080p. Major TV networks don’t use it yet because it requires a lot of bandwidth.

If you can afford a set that can handle 1080p, you might want to buy it so that you are ready in case a lot of 1080p content one day becomes available. You might also want a 1080p set if you are a videophile; have an enormous screen or a projector that fills a large wall; or if you play a lot of Blu-ray discs and believe you can discern the difference on a typical-sized screen. Otherwise, you could save money by buying a 720p set and you might never know the difference.

In 2006, you recommended a powerline adapter for Internet access by Netgear, the XE104. Is this still a good buy or are there others by now that are better?

I haven’t tested powerline adapters, the gadgets that route computer networks over standard home electrical wiring, since that date. Netgear and its competitors — such as Linksys and Belkin — have, naturally, come out with newer, faster units since then. But I am still personally using the XE104 successfully and feel I continue to get my money’s worth from it. It is still being sold. The newer units typically have greater speed in order to do a better job of streaming video around a home, but they work in basically the same way.

I have a Windows XP system, and things work well with my cable modem in my office. But when I’m on the road using Wi-Fi, I can receive emails, but can’t reply or send out. Any idea on how to resolve this problem?

This usually happens because the Wi-Fi provider is blocking the outgoing email server (called an “SMTP” server) that you or your IT department has set up in your email program. Some providers block all such outgoing servers. There are a number of possible solutions. The simplest is to use a Web-based email service, like Gmail or Yahoo Mail, or the Web-based version of your usual service. If your email is provided by your company, you may be able to access a version of Microsoft Outlook over the Internet that will work.

Another possibility is to ask the provider at the hotel or airport what SMTP server it does allow — usually its own — and enter it into your email program’s settings, if you know how. Yet another option would be to use a data card from a cellphone carrier, which I have found can usually overcome this problem. There may be other workarounds, and I invite readers to suggest them.

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

My mother is 80 years old and would like to purchase a device whereby she can send and receive emails only. She does not surf the Internet. Do you have any suggestions?

Unfortunately, I don’t know of a simple gadget, like the now-discontinued MailStation, that just sends and receives emails. However, there is a service and device, aimed mainly at those seniors who aren’t comfortable with computers or smart phones, that allows the receipt of email, and even photo attachments. The drawback is that this system is one-way — users can receive email and pictures but can’t send emails.

The service is called Presto, and it uses a special Hewlett-Packard printer that connects to a phone line. Your mother would receive a Presto email address, and any emails and photos sent to her would materialize as printouts. A broadband connection is neither required, nor compatible. The device costs $100, and the service costs $100 a year, if paid on an annual basis, or $10 a month, if paid monthly. Information is at presto.com.

I have boxes and boxes of old photos, and about 20 home videotapes and old movies. Some of the photos are fading and showing wear, so I would like to find a company that can convert them to a DVD. Doing it at home would take too long. Have you reviewed such a company?

. Some years back, I reviewed and recommended a service called YesDVD, from a company called YesVideo, that converts videotapes, movie film and photos to DVD. It worked well in my tests. The service operates through retailers, such as Walgreens, CVS, Best Buy and Costco, where you drop off your materials and then later receive the DVD, plus your original stuff. More information is at yesvideo.com.

I enjoyed your review of Xobni. Will it work on Outlook Express or Entourage?

No. Xobni, which creates personal profiles and social networks from your stored email, doesn’t work with Microsoft Outlook Express for Windows or Microsoft Entourage for the Mac, or for any email program other than Microsoft Outlook 2003 or 2007, on computers running Windows XP or Windows Vista. The company is working on a version for Yahoo Mail.

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