When I insert a backup copy of a DVD, it is rejected, it never mounts on the desktop or open DVDplayer. The same DVD plays fine on my G4 400; not on my G4 500... both computers run OSX 4.4
Are you sure that the 500 MHz G4 actually has a DVD-ROM drive? Check in the System Profiler and see what it says there about the optical drive on that particular Mac.
