Try using the DEFAULT NVDIA DRIVER PACKAGE FOR VISTA 64. The one you want is the 163.19 OR 169.75 . I had simalar issues using the driver supplied with my card. Used the NVIDIA PACKAGE and have had no Problems.. Here is the link for archived drivers...
http://www.nvidia.com/Download/Find.aspx?lang=en-us
If the problem Persists AFTER installing the NVIDIA DEFUALT DRIVER then you most likely have an Issue with the Vid Card..
However, there is one other Possible issue You may be experiencing and that May be a Conflict with SPD (SERIAL PRESENCE DETECT ) I am not sure wheter the CORSAIR XMS memory supports SPD.. If it does nto Support SPD then you may be having conflicts due to this.. VISTA 64 and 32 Seem to be Very Finicky about this Point.. If your RAM does not Support SPD ,, VISTA does not play well..SPD controls the DEFUALT TIMINGS For RAM as well as SETTING the Proper VOLTAGES for the RAM.. RAM that Does not Support SPD has to be Manually Set and May or may not Work as Desired...
Their is one Type of DDR2 and DDR3 that I know Supports SPD and that is RAM put out by KINGSTON. I learned the Lesson of NON SPD RAM the Hard and Expensive way.. i originally Purchased 8GB of DDR3 1333MHz by OCZ and it NEVER worked right,, In my Research into the Issue I found that OCZ DOES NOT support SPD..I switched to KINGSTON which Supports SPD and have had ZERO ISSUES.. I Spent over $ 1,000.00 To learn this Lesson..
Hope this helps. Good Luck..