There are a few caveats. ATI with crossfire or one card can, nVidia with SLI can with Big Bang Drivers, nVidia can without SLI enabled on older drivers. Vista 64 bit can have problems with VPU recovery with either brand and two monitors. Mostly ATI I think, but there are some reports of nVidia cards doing it also. You get a driver stopped responding and about 4 VPU recovery and then a BSOD. This is while at the desktop, not gaming. It's hardly universal, but I got VPU recovery and disconnected the second monitor. Never had problems on XP with two monitors. Vista SP1 didn't fix it.