My PowerBook isn't running OS X 10.5 yet, I don't think I'll bother with the new operating system tonight. I'd have to copy 10GB of music back to it.
As for the GPU in my Power Mac, I think it's an ATI Rage 9000 Pro or something like that. I haven't looked at it for a while. It's the one with 64MB of video memory.
Before you change any settings regarding QuartzGL, read the whole thread. Intell posted some system requirements on enabling it.