Pardon me if I have been too enthusiastic lately about Ubuntu Linux, but after installing it on my iBook, I am an even bigger fan. Great distro!
To install it, I connected my iBook to my desktop Mac with a firewire cable, and booted my iBook holding down the "t" key to boot the iBook as a remote disk. I then ran iPartition (commercial product) on my desktop Mac to free up 9 gigabytes for Linux partitions on the iBook. Using the PowerPC Ubuntu install CDROM, installation was a snap and now my old iBook just increased in value to me. I have an old style airport card, which Ubuntu recognizes - newer iBooks with 802.11g airport cards loose out: the manufacturer for the newer card does not release driver specs.