It is possible to easily enable Quartz Extreme (QE) on G3s or G4s that do not have a QE compatible AGP 2x graphics card. The hack is described here. From some tests that users did, it seems that only the G3/G4 machines with 66 MHz PCI bus saw some acceleration. Machines with 33 Mhz PCI bus, did not. The hack would work only if you have a Radeon or a GeForce2MX+ card, because they share the same driver with their AGP versions (QE only works on Radeons and GeForce2+ — ATi Rage cards do not work at all with QE, with or without hacks). Also, please note that users who enabled QE on their unsupported PCI machines, had major artifacts on some applications, most notably iTunes’ visual playback (quite possibly because the PCI bus is not fast enough for what is required).