This hint is for you if you have a graphics card that is having problems with Quartz Extreme, and are having trouble disabling it. Or if you have a GeForce3 card in an old Sawtooth G4 and are getting flickering problems, then here is a simple way to disable Quartz Extreme which is most likely the cause of this problem.
Use pico or your favourite text editor to edit the file: /System -> Library -> Frameworks -> ApplicationServices.framework -> Versions -> A -> Frameworks -> CoreGraphics.framework -> Versions -> A -> Resources -> Configuration.plist (you'll probably need
sudo to edit the file).
Look for the key
GLCompositorMinimumVRAM and change its value to a value higher than how much RAM your graphics card has. So if you have a 64MB card, then 128 should work:
<key>GLCompositorMinimumVRAM</key>
<integer>128</integer>
This may work with other key values, but this is the only one I have tried. This means OS X won't use Quartz Extreme unless the card has a minimum of the value you specified. Hence disabling it for your card. After the value is changed and saved, all you need to do is reboot and Quartz Extreme will no longer be enabled.
[
robg adds: I haven't tested this one!]