It all depends on WHAT you're trying to do. If you like remote administration services and a nicer-loking UI, then go for WinXP. If all you need is a straight-forward OS with no specific remote administration needs, stick with Win2k. Essentially they both run WinNT kernels, so thier stability and reliability is almost the same. I like Win2k myself better because its more "straightforward" than XP. Also, Xp has a built in firewall that might be a pain to disable or configure sometimes. Make your pick!
 
btw, is Win2k Sp3 out yet?

Shassounehs comments are right on target, I'd only add a few conciderations:
 
If you are about to buy the OS (as opposed to just asking a hypotehical question), you might as well go for XP, but be aware - by buying XP you support the quite likely MS scheme to turn your PC into a small pay-Bill-per-minute-used machine. Product activation is only the first step in this direction. You'll also have to contact MS everytime you switch PC (or major parts). And Big Brother will be watching you, just in case you believed that you can install the OS you bought on say both your desktop and laptop. If you ever want to sell your copy of XP I guess it could be worthless, because Big Brother will not believe that the buyer really bought it.
 
H.

That is true, although the new features of XP may or may not be of use to you. I guess it all depends really on WHAT YOU NEED THE OS to do. Define your needs and with it you can pick an OS!