Guess I'll post here since mine is 64 bit as well.
I'm having a problem with my (Sapphire) ATI Radeon HD 5750 when using HDMI. When I first built this computer, HDMI displayed fine. When I installed the latest drivers from the site, however, using an HDMI cable results in creating a vibrant, messy tie-dye effect on my screen to where you can barely make out where everything is on the screen. When booting up it displays everything fine, but once Windows comes up, the "tie-dye" effect kicks in.
I've tried 10.2/10.1/9.12/9.11 all the same results
I've tested a couple HDMI cables, so it's not that. My best guess is the drivers somehow?