In general XP is an improvement* over Win2k. Especially in boot up times. Some possible downsides:

a) Driver support for older hardware - shouldn't be a problem in your case as the machines originally shipped with XP
b) XP henerally needs more RAM than 2k
c) XP generally needs more HDD space than 2k

* Actually, IMHO once m$ got their act together with service packs for XP (tok 'em several years) it became the best version of Windows ever shipped - not excluding vista.

--=-- My credo: If it's worth doing, it's worth overdoing - just ask my missus, she'll tell ya laugh --=--
You're only paranoid if you're wrong!