Christoph,
I don’t have an answer to your specific question, but, I think you might want to reconsider editing EX footage on a G4 Powerbook. I’m doing various tests right now with my own Powerbook, and, although everything works (even though it’s not supposed to), the rendering and conforming times are astronomical. Right now, I’m attempting to encode an 8 minute sequence to an SD mp2 file for a DVD. No matter whether I export directly from an XDCAM sequence, or copy that timeline and drop it into an SD-DV sequence, Compressor is telling me that it is going to take at least 3 hours to encode my 8 minute sequence. That’s on a 1.5 ghz G4 Powerbook running FCP 6. I’ve got a same-day edit coming up soon, and I know I’m going to think about either taking my MacPro or buying a new MacBook Pro before then.