Step 1: iBook off, Powerbook on with iTunes off
Step 2: connect iBook and Powerbook via Firewire cable
Step 3: start iBook while holding the "t" key (this will mount the iBook drive on the Powerbook as a firewire drive)
Step 4: navigate to the Music folder on the iBook.
Step 5: Within that folder there is a folder named "iTunes". Copy this folder into the Music folder that resides in the Home folder of your Powerbook.
note: this will erase any music you have on your Powerbook and replace it with that of the iBook.
If you have any other questions, feel free to ask.