I am having exactly the same problem. My spec is:
Intel Quad Core 6600, 4Gb RAM, 2xGeForce 8800 GTX in SLI config, VISTA 64.
The game is unpatched, from a British DVD (no add-on yet).
I tried the fix suggested, but it is still the same. Is there really a way to play the game in 64 bit? I am losing confidence...