Currently Being ModeratedNov 21, 2013 12:38 AM (in response to akallenberg)
Highest (officially) supported Mac OS X is Tiger 10.4.11, for a G4 Mac below 867 MHz. You won't be able to run any recent app that requires an Intel-based Mac. It is also downloaded from Mac App Store, which requires at least Snow Leopard (10.6), and the app may require at an even later release.
"Writing" is an activity that the TiBook can handle easily, but just not with that app. If you want to use iBooks Author, you'll need a much more recent Mac.
One way to offload your files, even if it does not boot, as long as the hardware is not broken, is to use FireWire Target Disk Mode
You'll need another Mac that has a FireWire port, or a Thunderbolt port converted to FireWire. In FireWire Target Disk Mode, your PowerBook acts like an external drive that you can connect to another Mac. That other Mac reads and copies off your files.