i would say just take a pc that is compatibel with vista but with xp on it. Vista has a lot of bugs for the moment.
wait 6 months then vista. barely anyone has decent drivers for vista and the computer requirements are quite steep not to mention bugs. let microsoft release a service pack or something before buying it.
Well i'm going to get vista anyways cus my uncle works for Microsoft and gets vista ultimate for 45 bucks.