TBH you need to use target disk mode which requires a FireWire connection.
If you don't have that, you can use "sneakernet" i.e. an external hard drive (it will need to be FireWire to be able to boot on the iBook/PowerBook).
The only way of doing this is to clone a working Intel boot disk in 10.5 to an Apple partition scheme disk (either your internal Hard Drive or the external drive) using superduper or Carbon Copy Cloner.
If you installed directly to the iBook/PB's HD then you are done.
If you installed to an external hard drive, you then boot your iBook/PB with the external HD plugged in. Hold down the Option key and select the external HD and it should boot into Leopard using the External HD.
Then clone from the external HD to your iBook/PB's HD.
Then shut down, disconnect the external HD and reboot your iBook/PB.. You are done.