Just bought a 120gb seagate hdd in a usb case. Got it from ebay. It came pre intalled. Works fine on my windows PC. But cant get it to work on my iBook G4(osx10.4). The hdd shows in the finder and I can read anything from the drive but am not allowed to write anything on it. I`d got it for the ibook only. Please tell me how cud I get it to work.