Well, here's the deal...you can buy an external firewire drive enclosure that will fit notebook size hard drives, such as the ones that come out of the PowerBook.
But if the drive is in an existing PB and it has firewire, you can make it a firewire slave drive by pressing and hold the T key when the PowerBook starts up, this is called Target Disk mode. As soon as you see the FireWire logo on the screen, you can let go and attach it to another PB. The slave will appear on your other PowerBook as a hard drive, and you can do what you need to do. When you are done with the slave, eject the disk on the PowerBook by dragging it to the Trash, and then holding the Power key on the slave PB until it shuts off.