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?