Adaptor/convertor parts for HDDs?
The difference is the HDD connectors. The iBook G4 uses an IDE (aka PATA) connector, whereas the MBP uses SATA. Unfortunately during a quick google search I wasn't able to find a SATA to IDE adapter that would fit inside the laptop case. It's probably worth looking for second-hand IDE hard drives or contacting someone at Apple to see if they have a better idea. If you want to buy a drive, try starting here: Ebay IDE laptop drives. Let me know if you have any questions or if I got any of my information wrong.