The G4 400 is really at the lower edge from a graphics performance standpoint. OSX is a very demanding OS and PT 6 is a large app designed to prioritize audio performance first and graphics second. Most folks will see marked improvement in graphics with Dual Processor machines and machines above 1 GHz. DigiCS
Surchur, I have also seen similiar issues when using incorrectlty formatted drives. Did you reformat all of your drives with Disk Utility in OS X as HFS+ volumes? Also, make sure you try all of the suggestions on the following link: Mike