I have a feeling that the main reason is that you are using Vista 64. It has more bugs than Vista 32 and the hotfix probably still wont work. I have an NVidia card as well and have had no problems on my Vista 32, none whatsoever. If the sli fix doesn't work, I don't know how much more advice I can give.

I get the same thing sometimes. It's happened on all patch versions, XP x86 and XP64. various up to date nvidia drivers, single-core cpu, dual core-cpu. nothing prevents it... thing is, eventually, sometimes in a few seconds sometimes in about a minute, everything just starts again and it's as if there was no freeze. weird. I can't predict when it happens, and it doesn't happen every session. I run a single 7900 GS video card on a MSI K9N platinum. when it's frozen, I can't Alt-tab out of it. only realized it eventually 'caught up' and started working normally again because I was reluctant to reset the PC the first time. one more thing: background processes are still working, for instance, if I have winamp going in the background, the songs keep playing fine, just Sins and the keyboard/mouse are frozen. I haven't seen this happen in windowed mode. I pay full-screen at a resolution equal to my desktop resolution, 1600x1200.