Booting from the network is rather easy, and it is a nice thing to have
set up in case you might need it in a situation like this. Both of my
desktop machines at home are set up to boot from each other in case the
root disk fails on one of them, and it is really helpful when I need to
boot from something other than the normal root disk.
Here is a guide on how to boot an iBook G4 from USB:
http://ben-collins.blogspot.no/2010/08/booting-your-ibook-g4-from-usb-stick.html