I have a PowerBook 1,67Ghz 15" HiRes, the A1138 model which I managed to buy without a DVD drive. I also have an older PowerBook with a working optical drive, and I put that drive in the A1138. It was working with Linux in the A1138, and it was working with MorphOS in the old PowerBook, but not with MorphOS in the "new" machine

Yeah - but for sure I asked again, because in this case the behavior of this PB and/or CD-drive is very strange. Running with Linux, but not running with MOS in the same PB, without any change of hardware - that's not easy to explain.