I "only" have a 79xx graphicscard and concerning Microsoft being honest about System Requirements, I want you to show me a game that runs and looks like it does in promotion videos when you barely meet the minimum requirements...
Apart from that, I had the beta running on an Athlon XP 2400+ with 1GB of RAM and a 6600GT, with AeroGlass on and it worked, I also played games on it and it worked...
It's just my experience of course, but for me it worked, although it could take half a second for the start menu to pop up or so.