It all depends on what kind of computer you want.
I have 3 computers in my house. Laptop with XP, Desktop with XP, and Desktop with VISTA.
I must say I really enjoy the interface of vista alot more then xp or any other. It runs very fast and I can have over 20 tabs open at once ((doh) not kidding). But the thing I like most is that unlike what many people say, it is very stable (boom07). In older windows whenever one tab froze the whole computer would lockup. In XP it is rare, but does happen. I have been running vista ever since it came out and have never had it crash or lock up. Ctr+Alt+Dlt can get out of the program and close it no problem (even if it is a game).
BUT......you need to have a hefty computer to have it run correctly and to its full potential.
I built mine from scratch:
22 LCD monitor
AMD AthlonX2 64 5200.
320 GB SATA HD
ASUS Mobo
NVIDIA GeForce 7950GT video card
4 GB of ram (with 2 slots open for 8GB max ram)
And alot more (has 3 medium fans, 3 small fans, and a heat sink too keep it cool).
I built it primarily for multimedia, gaming and engineering programs (CAD and such). The only problem I have had is there are still some drivers that are not set up for VISTA, especial if its for older things, like my 6 year old printer. I say unless you have alot of ram, good video card, and better than average computer skills, stick with XP for now. I for one am sticking with VISTA.