convert from G4 to G5 ?

Hi, xs. No, it isn't possible. Apple itself, even starting with a blank drawing board, was never able to build a practical notebook computer around a G5 processor because of excessive power consumption and major cooling problems. Inserting a G5 into an existing design would pose even more formidable difficulties. If a G5 Powerbook were in the realm of possibility, Apple would have produced it long ago.

Hi again. No, all the MacBooks (which replaced the iBooks) and MacBook Pros (which replaced the Powerbooks) use Intel processors that run cooler and use less power, but are substantially faster than the G5s. That's why Apple switched to Intel processors in all its product lines a couple of years ago. If you want to use Adobe CS4 on a notebook Mac, you'll need one of the Intel-powered ones.