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 keeping multiple computers in sync, waiting for Microsoft Vista and installing multiple security programs.

I travel among three locations and I currently lug an eight-pound Dell laptop. I would like to change this to having “permanent” PCs (either Windows or Mac) at each of the three locations. What software can I use to keep them in sync?

I recommend a product called FolderShare (www.foldershare.com), which is now owned by Microsoft, or a competing product called BeInSync (www.beinsync.com). Both do the job, though they differ. FolderShare can synchronize selected folders among groups of computers, including mixed groups of Windows and Macintosh computers. For instance, all the files in your My Documents folder on a Dell can be synchronized with all the files in the My Documents folder on an HP, or with all the files in the Documents folder on a Mac. But it doesn’t synchronize contacts and calendar items in Microsoft Outlook. BeInSync doesn’t work with Macs, but it does synchronize Outlook items, in a limited fashion.

I was considering buying a new PC now but was wondering if I need to wait until Microsoft Vista is released. I understand Vista only works on certain PCs. What is your advice?

My advice depends on your needs. PCs preloaded with Vista won’t be available until January, 2007, and possibly later, if Vista’s release date slips again. So if your current machine is essential in your life or work, and is on its last legs, or is seriously failing to meet your needs, you shouldn’t wait. But if you can go another six to nine months with your PC, I’d suggest waiting until you can buy a machine with Vista preloaded.

It is certainly possible to get a computer now that can be upgraded to Vista. But with any major new Windows release, there can be surprises and quirks in the upgrade process. Preloaded factory machines can also exhibit problems with a brand-new operating system, but they are likely to be fewer than what an upgraded PC would experience. A factory-loaded Vista PC may also be cheaper, because you will very likely have to add more memory to a current PC in order to run Vista well.

I have just installed a new security program that has both antivirus and firewall protection. To install it, I had to remove AdAware, Spybot and Microsoft Firewall. My question: Is one program enough, or should you install multiple programs to insure safety?

First of all, two of the programs you removed, AdAware and Spybot, perform a function your new software probably doesn’t — they detect and remove spyware and adware. Antivirus and firewall programs don’t typically do this. So I would re-install them and use them.

However, I don’t recommend using multiple antivirus or firewall programs, and neither does Microsoft or the major security-software vendors. Redundant programs can get in each other’s way and cause conflicts and confusion. The result may be that some malicious software sneaks through or that some innocent files are blocked. So pick one antivirus package and one software firewall and stick with them.

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Because of the volume of email I receive, I can’t routinely answer individual questions by email, 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

Some people place files on a portable device, and then manually copy the files to all their PCs. Others email selected files to themselves. But these methods are time-consuming and imperfect.

Now, new services can automatically keep certain folders and files synchronized among your multiple PCs, without any work on your part.

These file-synchronization services aren’t free, and they do take a little effort to set up. But once they are up and running, the effect is like magic. Within minutes, or even seconds, after you have added or deleted or altered a file on one of your computers, the change is perfectly replicated on all your other machines.

There are three main contenders in this budding field. One, called Groove, available at groove.net, is owned by Microsoft. It’s mainly designed for collaboration work in big corporations. Two others, BeInSync and FolderShare, are aimed directly at consumers and small businesses. BeInSync is from an Israeli company called BeInSync Ltd., and is available at beinsync.com. FolderShare is from an Austin, Texas, company called ByteTaxi Inc., and is available at www.foldershare.com.

The best choices for consumers are the two consumer-focused offerings, BeInSync and FolderShare. Either will work well in most cases. But for this review, I concentrated on FolderShare because it’s faster and more flexible. In particular, it’s the only one that works on both Windows and Apple Macintosh computers.

Here’s how FolderShare works. Starting with one computer, you select the folders you want to keep synchronized. You link these folders to companion folders you select, or create, on the other computers, and install the service’s software on each machine. The software, which runs quietly in the background, transfers files, as needed, among the machines so the contents of those folders remain up-to-date and identical on every computer. The transfers, done over the Internet, are fast, invisible and encrypted for security.

Over the past few months, I’ve been using FolderShare on six of my computers — three Windows PCs and three Macs. Two of these computers are in my office; three are in my home; and one, a laptop, is often with me on the road.

I set up FolderShare to keep five different folders, containing over 36,000 files, synchronized, and it did so without breaking a sweat. For instance, I linked folders called “columns” on every machine, and linked the “My Music” folders on my three Windows machines to the “Music” folders on my three Macs.

Now, all the latest versions of my columns and notes — including those in Microsoft Word, Excel and PowerPoint files, and Adobe PDF files — are on all my Windows PCs and Macs. So are all my music files, my photos and my videos. After I wrote this column on my laptop in California, it was instantly replicated on all my other machines on the East Coast. (The use of broadband is highly recommended for speed.)

FolderShare did all this without slowing the performance of my computers, except for the first few hours, when it was moving thousands of files around in a short period.

FolderShare can handle older versions of Windows back to Windows 98. BeInSync works only on PCs running Windows XP or Windows 2000.

There are three versions of FolderShare; each can be used with an unlimited number of computers. The free “basic” version allows you to synchronize two folders, with up to 500 files in each. The personal version, at $50 a year, expands this to 100 folders with up to 20,000 files in each folder. The professional version, $100 a year, allows 250 folders with up to 50,000 files in each. It’s also speedier than the others.

FolderShare also allows you to invite groups of other users to share some or all of your synchronized folders. I tested this and it worked well. In addition, in the top two versions, you can tap into your computers from any Web browser on any computer to retrieve any file. This feature also worked fine in my tests, but you can disable it if you are worried about outsiders gaining access to your files.

If you have desktop search software on your computers, FolderShare can do a unified, combined search for files across all these machines.

FolderShare doesn’t keep copies of your files on its servers, but it does keep records of your computers, and the folder and file names being synchronized. It can provide a form of backup; your key files are on other machines if one fails or is stolen. But take care to guard your password, as anyone who learns it could access your files by logging into your account.

BeInSync has one major feature FolderShare lacks. In addition to synchronizing files, it can synchronize some of your email in Microsoft Outlook, and your contacts in Outlook and Microsoft’s Outlook Express. BeInSync also costs less. Its top version is $60 a year, or $100 for two years.

FolderShare is so useful and works so well that I recommend it or BeInSync for anyone who needs key files kept up-to-date.

• Email me at mossberg@wsj.com