Hi guys. You may remember I was one of the originals to put a 8800GTX in my mac pro under windows. I have recently upgraded my mac pro with a new Ati 4870x2 card. I wanted to post because some of you may want to do this for the pc side to game so lets get to my findings. First of all, I installed the card and hooked it up from the power cables coming off of the cd drives just like I did my nvidia 8800gtx. THIS DID NOT WORK FOR ME. The machine would turn on and chime but upon boot would shut off completely or go into a power down state. From what I can tell, the PSU will not handle the new 4870x2 card being powered by the lone cd rom power cable. Now, being I wanted to use this card while I build my gaming pc, I had a spare 500w BFG PSU lying around to test if indeed the mac pro PSU was the problem. I rigged the external PSU with a thick paper clip. Take one end and plug into the green pin on the MB connector and take the other one and plug it into a black pin. This powers the PSU without having it hooked to a computer. I now plugged it into the vid card and powered on the external PSU. Upon turning on the mac pro, viola....it booted and works perfect. I know. its not a good idea to run it like this but it does work. I wanted to let others know my findings with the original mac pro as I know alot of you use windows on it to game. I have the original Mac Pro 2.66 with 6gigs ram, 3 hd's, a blu ray burner and now the 4870x2 card. It plays really well for the betaish drivers on the video card. Oblivion plays at 2560x1600 with 12x effective Anti-Aliasing and 8x AF better then the 8800gtx did. Hope this info helps someone out.