There are a few different Linux versions which may work on some
architectures of Macintosh computer. Before you do anything, be
sure you can make and have a bootable full system clone on an
externally supported (FireWire 400) hard disk drive. A self-powered
one with AC power supply is best, then it is independent of the Mac.
Not all externally enclosed FW HDD units are capable of booting
an OS X system or full clone. You can get clone utilities by the names
of Carbon Copy Cloner, or another favorite, SuperDuper. Downloads.
Some people have reported issues and damages to their Mac OSX
installation when they've tried installing a Linux version on there, too;
so be ready ahead of time and also know when to try some other
Linux version if you find one that does not work with your computer.
Names like YellowDog, Debian, Mandrake, Gentoo, Ubuntu, & others.
Some of the names and versions I've found in a casual search may
have changed somewhat. If you find information from some internet
older discussions at non-Apple forums about these non-Apple OSs,
be aware they may not be able to run adequately in your iBook G4.
A most general search will find a cross-section of some stuff; here's
one where I keyed some words into the google search engine...
' Linux ubuntu gentoo for Mac G4 ' - a google search:
http://www.google.com/search?hl=en&q=Linuxubuntu+gentoo+for+Mac+G4&btnG=GoogleSearch&aq=f&oq=
If the computer has a large enough hard disk drive in it, a partition
scheme may be employed to facilitate keeping OS X on one part
and some other experimental system on another. This may allow
you to dual-boot between a known stable Mac OSX system and
some questionable & experimental beta-like effort you find online.
There are probably few if any outright advantages in a Linux OS
based system not already superseded by the great and powerful
Mac OS X. If you like tweaking and keyboarding around, there is
Terminal and other accesses into the underpinnings of BSD/Unix
within the Mac. You can learn quite a bit about many similar OSs
by getting into Mac OS X at a non-graphical level more often.
Some of the Linux versions available are download disk images
you'd burn to a CD for later installation; other ones will ship a
DVD or CDs, these sometimes have a fee for the discs, etc.
If you look into some of the Linux for Mac (be sure they work
on PPC architecture) sites, some of them have forums, too.
In any event...
Good luck & happy computing! 🙂