My wife and I have the same hardware spec except for the video card.. she has a 7900 GTO and I have a 8800 GTX ... she isnt able to lauch to instance of a 3D game.. as I'm able to launch five at a time...
I've done some research, but no luck so far... hang on .. it's pissing her off... I presume that your are too...
I'll keep diging...