Aright its all like this..
Vista will require two things. 512mb ram. DX 10 compatable video card.
There are going to be like 4 or so versions of this. Each one uniquly different as I have heard. But aside from all that, the video card thing is simple. You will be MADE to buy a new video card for Vista. Because no current video cards are compatable with Vista. So if you drop 600 on CF'd Ati X1900XTX's your SOL. Because they just wont support DX 10. Gay...