I was trying to figure out if I could mix the ATI 2600XT with the NVIDIA 8800GT in the same mac pro since I had heard that mixing drivers on the 2006 and 2007 Mac Pros was a problem. I checked Apple's Video Developers Note and found that any reference to this incompatibility on the 2006-7 Mac Pros was removed (problem solved?). I called Apple Sales support about my order, first trying to squeeze more accurate ship info on my Mac Pro before I downgraded my configuration to the ATI 2600XT. I got transfered to technical support and was bounced around for well over an hour. Finally, I got the guy to do a round table consult over iChat and here is what the video guys had to say. They didn't see any reason why there would be a problem for me to use 4 displays running processing off the NVIDIA 8800GT in slot 1 and using an ATI 2600XT in slot two for extra outputs, but the caveat is that the guys who this answer came from don't have the 2008 model, so no 100% guarantee it until the 8800GTs were available. I'm sticking with the 8800GT for now, and when my tower gets here, I'm going to bring my card to an AppleStore and see if I can convince them to let me pop it in slot 1 on a standard build floor model to test compatibility. What would be really nice is if some benchmarking site out there would test a Mac Pro with two 8800GTs versus 1x8800GT and 1x2600XT to see if there are any performance issues introduced by using the two drivers.