In my experience, the way the iBooks and Powerbooks are built, you are stuck with what the case has to offer to fit a mother/logic board in it. 12in iBooks can only fit mother/logic boards for the 12in case - from 500MHz to 1.1GHz, the same with the 14in iBooks, and 12in, 15in, and 17in Powerbooks. The good thing is on can upgrade their iBook/PowerBook with a faster motherboard but you are stuck with that particular models of choice because of your laptop's case.

Ebay is not the only place, there are many places you can go to online for a motherboard, thing is are you willing to pay such costs. Wegenermedia ( wegenermedia.com ) sells parts and does repairs for newer PowerBooks (G3/G4 to current Intel models) but they are priced higher than Ebay. Only good thing is that they guarantee their parts and work for up to a year, Ebay does not.