Installed Leopard on my Powerbook G4 - all was well until plugged in Passport external hard drive to USB port - just kept clicking and wasn't recognized. Tried my PC and son's Macbook worked fine. The problem? Powered USB ports on G4 are too weak. When I used a self-powered USB hub .... presto - all is well! I wish the documentation warned me it would have saved me a lot of time on Apple and Western Digital websites.....