I usually take it easy on the weekends, but I'll try to make a quick weekend edition post when I have the chance. I'd like to take this chance to remind you all that many computers from the 90's are still useable today.
Chances are, many of you have an old computer stashed away that's close to 10 years old. By 1998, PC Desktops were already approaching 500 MHz. I have several machines like this. You might think they're sluggish, outdated, or whatever, but they're probably just not up to all the tasks that you're used to doing now. Computers of old are not geared for playing the latest and greatest games, playing high-res content from YouTube or Google Video, or things like that.
Think back to what you did with them. Think of what the Web was like back then. If you want, check out what Yahoo!, CNet News.com and JPL websites looked like in '97 (click the links to see). While websites have come a long way, realize that these were cutting edge back then, and didn't demand much from your system.
Windows 2000, Fedora Linux, Ubuntu Linux, or FreeBSD are operating systems that should run pretty well on anything down to 400 MHz, if you stick to simple web browsing, word processing, and e-mail. They also happen to make great computers for students. They won't be able to play the latest and greatest games, but it's likely you won't want them doing that in the first place.
Most of the systems I've covered so far are a little "exotic" so to speak. I could go on writing an article per day for 2 months straight if I went into details about every bland 1980's/1990's PC I've got scattered about. The fact remains, however, that older PCs can still be useful these days, even if it requires finding a new hard drive or a network card to bring it up to some standard of functionality.
Keep your expectations reasonable, and keep in mind what they were capable of back in their day.