Sure its possible, but you will run into a lot of problems and will prob. have to do a lot of cutting in the G4 case to get everything to fit. The beige g3's dont have firewire or usb. they have the old style ports. The mother board is totally different and a lot of modifications to the G4 case wil need to be made if you want to use the ports. I have a question though, why would you want to put the guts of a beige G3 into a g4 case? Doesnt make sense to me. But have fun trying.