I recently had to remove my Nvidia 9600GTOC video card because it was introducing random intervals of latency that resulted in pops & glitches. I used the DPC latency checker program to verify the long latencies. I had consistent latency of 30 or 40 microseconds with occasional periods of up to 2
seconds latency.
In the end I found that the only way to get rid of them was to go back to a 6600 based video card.
Digi Tech Support verified that there were issues with some new Nvidia cards but didn't comment about the specifics.
See
http://duc.digidesign.com/showthread.php?t=227313 for more info.
Jeff_C