Same problem with ATI 2600 XT
dont write this off as NVidia problem too quickly
I am having the SAME issue on my HP Laptop with ATI HD2600 XT
Did an "upgrade" from Vista 64 which was running perfectly
Had this issue, got the "new" drivers from Windows Update, did not fix it.
Installed newest drivers from ATI site, released 6/15/09.. did not fix it.
Hope MS will take a look at this issue as it does not seem to be limited to 1 model Nvidia card.
BTW, my desktop computer with EVGA 8800 GTX does NOT have these issues running same version RC7 64 installed from the same disk.