Back will give you a bit of trouble as the QS has an extra PCI slot. Need some case cutting. I'm sure It can be done, just some work. War is right about the PSU, its proprietary, though google around and check to see if anyone has used an standard ATX power supply with it, you would loose the Apple Display Connector but thats no big deal if you don't own an older Apple LCD. May be cheaper way to go.
PB G4 15" 1.2ghz - Pismo G3 400 mhz - iBook G3 500 "Jukebox"
"SawSmurf" G4 500 - Quicksilver G4 Dual 1ghz modding...