Ok. I've upgraded my Sawtooth G4 with an OEM GeFore 4 440MX. Worked fine under Jaguar, but after I installed Panther I get a black screen at startup and nothing else.
From what I've read so far on Apple's site, the only solution found is to either put the old video card back or use the drives from Panther after Jaguar installs. The downside being that Quartz Extreme may not be supported.