Ok, I loaded the Vista64 debug tools and then installed the latest 181.22 gefroce winvista64bit english whql drivers from Nvidia.
The system crashed to the BSOD (as expected) when I entered my password and the desktop flashed for a second or two.
Using the debug tools, and the symbols specfied in Bee_Dee_3_Dee's link:
the debugger says the crash is occuring in the dxgkrnl.sys module - the "DirectX Graphics Kernel". The tool says my current version is 6.0.6001.18000.
Hmmm, now what. I am running Vista64 SP1. I thought that had all of the latest hot fixes and system files.