Special notes for those who have already upgraded to 10.6.8 and have lost display functionality
If you still have access to a display (most cards still have DVI/VGA functionality), simply install the patch to your boot volume and restart.
Get the new 5xxxDriverPatch here.
In the case of a card that won’t boot (this seems to be the case for some 5770 cards), or if you depend on DisplayPort for your display, here are some recovery options:
1. Use another video card (remove the 5770) to boot 10.6.8 and install the patch.
2. If you have another mac boot drive or can create one, you run the patch from the other drive with your original drive as the destination.
3. If you have a monitor that supports analog, try booting in safe mode (boot with the shift key held down) with only the VGA display plugged in. You’ll be using the DVI-VGA adapter (on the DVI port closest to the CPU tray on the 5770 standard, DVI port farther from the motherboard on the 5770 single slot). Once booted in safe mode, install the patch and restart normally.