Should be compatible. The only issue is if you have a 17" powerbook (which requires a higher voltage power supply, 65W I think). Even then, I don't think the 17" power supply will screw up an iBook. The 12 and 15" supplies will be fine.
You might want to check out the support discussions for powerbooks, power/battery issues. Here's one thread on a related topic (not sure if this URL will work for you though).