Originally Posted by Ripper3
If you're looking for a career in the computer industry, or will be, I'd bone up on servers, so anything office based, may not be fun, but could give you a chance to put something truthful on your CV, that will be eaten up by potential employers. Plus, if you do ever need to mess with a server, you'd be basicaly prepared for it. May not be fun, but it's a start.
Otherwise, I'd just use it as a downloading box, a MAME/Emu machine, VM host as suggested (so you can then just try Linux, or osx86, or a Unix system, without installing it on whatever PC you would like to try it on.
Might seem like boring suggestions (cept downloading box, and MAME/Emu machine, which can lead to funfunfun!), but they're useful, and once you use them for such purposes, you'll probably be confused as to how you survived before trying it.
Other than that, just use it as a test machine. Plenty of things you can do with a PC, in software and in hardware, just need to try.