i believe the Cube's USB ports are special 10 watt ports... You can (at your own risk) use them on other computers but the volume will be lower. The Apple Pro speakers are different than the Cube's speakers in the fact that the imac's had an their own propriatary connection and no inline amplifier like the cube's. i don't know how you will get the extra power to the Cube speaker amp. but it would be cool. they are nice speakers.

also the Cube speakers when used would make the Cube run hotter. this might also be the case with your ibook. especially since you would also be putting heavier strain on the ibook's USB ports as far as power draw might be concerned.

2.4gHz 15" MacBook Pro, 1.66gHz Core Duo Mac Mini, 2.5gHz G5 QUAD, 733mHz Quicksilver, 450mHz G4 Cube, 700mHz G3 iBook, 350mHz Sawtooth G4, 350mHz Revs. A and B B&W G3, 16mHz Powerbook 100, 8mHz Macitosh Classic.