Better make sure u have XP pro and not XP home becasue home no workey with domain authenticating.
That being said, I am running XP pro machines ( all new 1.6Ghz Athlon XP machines, 256mb ddr minimum) on an NT 4 domain (company waay to cheap to upgrade to 2k server) and it runs fine. Would be much better on 2k server running AD as that is now the defacto IT industry reco standard for M$ networking.
I do disagree with hypnotic, you certainly dont need serial ATA (what 5 mobos acutually support it now, usb2 or any of the other stuff, just modern/fast hardware and u will be fine.
PS, dont forget to neuter a lot of the crap in XP. Less headache for you if u admin'ing it.
UPNP, SSDP, Imapi burning, etc.