I installed the OEM Radeon HD 4870 in a First Generation "Clovertown" 3.0GHz 8-core Mac Pro. It's working. This is the model I mean (see right column). http://support.apple.com/kb/SP30 (I pulled the card from a Nehalem.) I booted from the drive that came with the Nehalem. (Easier than cloning the system or trying to get the drivers to copy over - which gave an error on boot.) It runs with no problems. I'm busily running 3D Game benchmarks which I will report back on later tonight or tomorrow morning.