Apple recently released its developer note for the new Power Mac G4 towers, which offers a plethora of detailed information regarding the new systems.
http://developer.apple.com/techpubs/hardware/Developer_Notes/Macintosh_CPUs-G4/PowerMacG4/index.html
http://developer.apple.com/techpubs/hardware/Developer_Notes/Macintosh_CPUs-G4/PowerMacG4/index.html