Thanks Midnight, Ill give that a shot.
Cdrsubron7,
Here is a link for those MS hotfixes I mentioned.
http://www.nvidia.com/object/windows..._hotfixes.html
If you havent tried these yet they may solve you issue as they have worked for some folks getting the nvlddmkm error. Along with these, the first and easiest options are to flash the bios as Midnight said, update to latest drivers. Also, have you overclocked you cards or where they factory OC'd? If so you may want to dial them back as this has also been noted as a cause.
Other possible fixes:
Turn off User Account Control for Vista
Turn off Windows Aero
Turn of Dreamscape if you are using it
Check and make sure your power supply is up to the task. Most are suggesting at least a 750w.
Monitor you temps. This problem can also be related to heat. Rivatuner makes a nice program for that if you dont have one and also allows you to set you fan speed and OC your cards.
If none of this works then its time to start testing you hardware including your memory as I have heard that in addition to a bad video card this problem can also be the result of dodgy memory.
Worse comes to worse you may want to revert back to XP. Apparently, Vista is very fussy about things not being just right where XP was a bit more forgiving. I would wait till Vista SP1 comes out before doing that however since it is supposed to fix many issues.
Thats about all I can think of to try and its basically a rundown of everything I have done so far. Hopefully you will have better results than me.
Keep us posted on how its going. Id be interested if you come across a solution that works for you. I will do the same if I get my problem fixed.