There has been endless speculation on what this beast will need for wheels. Here's what someone from Microsoft has to say :

Nigel Page is a strategist with Microsoft Australia. He told APC today that Vista would work best on a video card with more than 256MB RAM, 2GB of DDR3 memory and a S-ATA 2 hard drive. Here's what he said, more-or-less verbatim (we left out boring bits).
http://www.apcstart.com/teched/pivot/entry.php?id=6