I have a G4 ibook. When I try to load Ros...

Isolate the problem to make sure its not the optical reader.  Get a music CD and try to see if it will play, then get a DVD out to see if it will play, then get another software disc to see if it will play.  Will all three play fine?  Then your Rosetta disc is fu.k.d up from heavy scratches, smudges, or corrupt manufacturing process. Otherwise, your optical drive needs to be replaced if it has problems playing the other discs.