So, here's the scoop. I ordered the HD2600 a while ago and got it yesterday, and quickly installed it. At first, the card worked with both OS X and Windows, but after I stuck my Leopard DVD in the drive to update the drivers because it wasn't letting me switch the screen to the maximum resolution, it stopped working. To describe: I turn on the computer, I see the initial boot screen, then the screen remains blank and I can't see anything. I can take a video of it if need be. I did try installing ATI's catalyst drivers and then hooking my Mac Pro up to two screens (one on the HD2600, one on the 7300 GT) to see if that would let me mess with the card, but that failed. So, any ideas?