I wonder if my problem is similar... I upgraded to Tiger and the latest version of iLife, but after using it once or twice, the Quartz effects stopped working. From what I have read, my card GeForce 5200 shouldn't even be compatible, but when I did another software update, it worked again! I even made a complete project, rendered and burned to DVD. Quartz just started working. Unfortunately it didn't last. After restarting my computer yesterday it is once again not functioning. Is this similar to what you experienced?
iMac G5 1.8 GHz Mac OS X (10.4.8) 2GB RAM
iMac G5 1.8 GHz Mac OS X (10.4.8) 2GB RAM