I would run Vista if my computer had 4gigs of RAM, a 120gig harddrive, and a GeForce 8800GTX
My old desktop, a 128mb GeForce 6600GT w/ a P4 Northwood 2.53ghz and 1gig of RAM slowed to a crawl with Vista installed. My laptop is similar, but it has a Intel Core Duo and a GeForce Go 7300. I figure it would be just as slow.
I will wait until I have a supercomputer, and a ton of DX10 games before I move over to Vista.