There is probably 0% chance that you would ever find drivers that would make that card work with OSX. You need a newer ATI or nvidia card, I would recommend a GeForce 2 [not enough support for the GeForce 3 to warrant the price yet] as your primary display [if you have an AGP port that is, I think the G4 "Yikes!" didn't have AGP...] and an ATI Rage Pro for your secondary monitor. The rage pro is relatively cheap and games [the real video hogs] will only use your primary display, so it doesn't need to be a super card.
Dual G5 2.0Ghz / 2.5GB Ram / 620 GB HD / 23" CD