A Powerbook G4 will likely not understand what to do with half the data on it, because the MacBook is a different setup. Do you have the original 10.5 installer disc that was used for the MacBook? If you do, boot off of it, and see if it can see your Time Machine backup through its Utilities menu for restoring via Time Machine. Connect the drive when it requests you do so. If it can, but it can't see the internal drive, then you probably need to first see if the internal drive's directory is damaged. For that you need to run the Disk Utility in the Utilities menu of the installer program for 10.5's Repair Disk. If it can't repair disk, go out and purchase Alsoft Disk Warrior. If it can't repair the disk, then yes the internal hard drive is shot. If one or the other can repair the disk, shut down the computer and eject the 10.5 disk holding the mouse button. It should reboot normally.