I have Vista 64 also. It is not an issue with the NVidia cards themselves but rather Vista 64. If you get the most recent updates to Vista and then get the latest NVidia drivers, it stablizes the open GL alot. Most of it is done by the Vista updates. 

I think Microsoft is finally starting to pay attention to Vista 64 now that XP is completely gone and Windows 7 seems to be a 64 bit primary OS.