Hello,
Nope, the iSub+Pro Speakers are only for PowerMac G4s (w/133 mhz and above busses), iMac Flat Panels, and eMacs. All of these have an internal amplifier for the Pro Speakers (they don't have their own power supply to power an amp).
If you want Apple-designed speakers for your iBook, the
harman/kardon SoundSticks are your only solution (the SoundSticks are the tall satellites and a subwoofer--
which is not the same as an iSub--the 2 are not interchangeable--though they look similar.
They sound great. I use them in my office. Not too bassy, but I listen to jazz most often at work.
Good Luck!