This week my mailbox contained questions about locking your files, buying a modest computer and building your own computer.I am looking for a simple Windows 98-compatible program that will allow me to lock a file or a folder so my son or his friends using our family computer don't take a look at some of my files and folders with personal info on them.

What, you don't want the kids to know you've been downloading Britney Spears songs from Napster? There are a number of shareware and freeware programs that perform file locking and encryption in Windows. I haven't tested any of these programs, but they include EasyCrypt ($49), Private Files ($25) and File Obfuscator (free). These are available at download.cnet.com. A huge listing of file encryption shareware for Windows is at winfiles.cnet.com/apps/98/encrypt-file.html.

Would the Dell Dimension 4100 be about the right power and speed for my wife, who uses the computer primarily to surf the Net, send and receive e-mail and other routine applications? She doesn't play computer games or listen to music on it. She is now using an old computer which crashes much too often and is quite slow.

The Dimension 4100 is Dell's mainstream consumer model, so it'd be fine for your wife. You can configure it in many ways, but the most basic version costs $999, including a monitor. A mid-range 4100 costs about $1,299, including monitor. However, I am a big proponent of only buying a PC that closely matches your needs. So, if her needs are as modest as you describe, and you want to go with Dell, I'd lean toward the less expensive Dimension L series instead of the 4100. It starts at $699, including monitor. Even if you doubled the memory on this base L model, to 128 megabytes; increased the monitor to 17 inches; and added a CD recorder and a network card (for a future cable modem), you'd still be spending only around $1,100 - and that includes the monitor and a free printer.

I am interested in any advice you might have to someone considering building their own computer system. Is this a bad idea? Is there enough of a cost benefit to even try?It's not necessarily a bad idea. It all depends on your skills and interests. I'd probably put the hard drive in backwards and break the Pentium processor somehow. But you're undoubtedly handier than I am. It's a low bar.

Seriously, my advice is that you should never build your own PC to save money, because it's hard to save much, especially if you put a price on your time. However, there are other perfectly good reasons to do so. It might be a hobby project, or you might be a finicky techie who is particular about the internal components, or you might want an unusual configuration you can't find elsewhere. One warning: I wouldn't advise embarking on this job unless you either have a good knowledge of computers or have the help of somebody who does.