First to give you a bit of a background on the Mac Pro itself: Mac Pro (Early 2008) 2 x 2.8GHz Quad-Core 16GB of Memory 8800GT 4TB HDD AirPort Extreme Card 2 x Dell 24 inch monitors The list stated above is not intended to be for bragging rights but just to give you an idea of what my machine is currently stocked with. I also utilized Bootcamp to install Windows Vista 64bit OS. This was required because I do work from home time to time and need Windows specific apps. At the same time, I also like to play games on Windows as well. I could play games on either my 360 or PS3 but truth be told, there are some pretty slick PC games out there that aren't available for the consoles mentioned. When they are available for either console, they usually don't get ported over to well, IMO. With that said, I ventured out in beefing up my gaming experience (on the Windows side) by getting the ATI 4870 card. I already knew that this card would not work in OSX. After scouring the various forums about providing additional power to this card, it was a success. So next, I ventured out in trying to figure out if I could keep both the 8800GT and the 4870 card plugged in at the same time with one monitor attached to each card. This would be a convenience since I wouldn't have to fumble with monitor cables nor unplugging cards. No such luck. The scenarios I tried, when booting into Windows, were: Switch GPU card slots: Results - didn't do anything. Plugged both monitors into 4870, while 8800GT still plugged in - when booting, blank screens, no video signal from Windows to use the 4870 card. Yet, can hear the Windows chime and etc. Disable/Uninstall 8800GT within the device manager of Windows: Results - doesn't recognize 4870 as primary card and uses VGA mode on the 8800GT . Keep in mind, both cards still show on the device manager. Make change in Windows bios not to recognize one of the GPU slots: Results - EFI-based and cannot access bios emulator...at least from what I have read. Unplug power cable running into the 8800GT and plug the second monitor into the 4870: Results - SUCCESS It seems like Windows only focuses on one video package and I don't think it likes two different cards from different vendors. There have been a few postings about having success with dual booting, without swapping cables or unplugging the cards, if both cards are of the same vendor. That's cool. I can only assume that the reason why the 8800GT card even shows up in VGA mode after disabling/unstalling it is because the card itself can work in both Windows and OSX....meaning the card's bios does the magic. I thought to myself "Well what if there is a way to disable the Windows portion of the card's bios so that it doesn't even get picked up"? I have no clue if that's even possible and the work behind it. But this scenario wouldn't be any different than a PC based card not being recognized in OSX. With all that said, all is not lost. For the time being, when I want to boot into Windows, I'll just unplug the power cable from the 8800GT. Minor thing, nothing big. When the 4870 Mac version comes out, I'll get that and run it CrossFire with the 4870 PC based card. I know Crossfire will not work in OSX and I'm not expecting it to. But before doing all of that, I'll be paying very close attention to the power requirements as well. Barefeats website has had success in using Crossfire with cards that require just as much power. So I can only assume at this point that I should be okay. That's my rant. I was a bit surprised that there wasn't a single resource on the web I could turn for this topic. But at the same time, I'm glad several postings did exist. I'd love to hear some of your thoughts and ideas on this topic. Maybe some of you have had different success in this area and would like to share. In any case, thanks for taking the time to read this long post.