That's disappointing
A few more ideas:
You do have Vista updated to at least SP1?
You aren't overclocking the CPU by any chance?
What PSU are you using? You might double check that all cables/plugs are firmly secured to the video card.
Are you launching crysis with the x32 or x64 .exe? Whichever one your using, try using the other.
Have you tried temporarily downclocking the card yet? It may worthwhile as a test.
To rule out RAM being an issue, it may also be worthwhile running memtest86+ overnight to see if it throws up any errors at you:
Memtest86+ - Advanced Memory Diagnostic Tool