I use an nVidia card in my work machine and had similar problems with it dying. I tried updating its drivers using Microsoft's driver and did not fix anything.
However I went to the nVidia site and got their driver and has been smooth sailing for a couple of years. Just a possible solution.
Had a look at their site and they have a lot of information about hotfixes and drivers and DirectX all involving Vista systems (
http://www.nvidia.com/object/windows..._hotfixes.html). Might be worth a read.
Good luck with it,
Jon
Monolith Entertainment