Logic Board quandary

I have an Onyx PowerBook G4 which came with a 550 mHz processor. I need to replace it, and was wondering what my options are? Is the best I can do is a 667 mHz processor? Also, the reason I'm replacing the motherboard is because the power supply is defective. Is it possible to repair the power supply without replacing the logic board? Can anyone recommend a place to have this work done?

You're probably better off investing in a newer Mac laptop. Even for something as old as a PowerBook 550, replacing the logic board may cost more than it's worth.