Ugh. Didn't these come standard with PCI Rage 128s? If not, and you don't want to splash out on a Radeon or better, pick one up. They're dirt cheap and worth every penny
Try for one with the black heatsink - I forget what the actual difference is, but they're more betterer for some reason. And there's a hardware DVD decoder daughtercard which is worth keeping an ear out for as well. OTOH, a Radeon can do that all on its lonesome.
Not sure that's literally true - I thought they were identical in performance at the same clock speed when the G4's Altivec intructions aren't being used.
Certainly in terms of bang for dollar, the same priced G3 would be faster in non-Altivec situations.
Also note Apple put in a eeeeebil firmware block to stop you installing (Apple branded ie second hand) G4 ZIFs in those towers, and you'll need to look up the software trickery to overcome it. It's not complex.