I just noticed on the Ubuntu Linux website that there’s an education oriented variation of the distribution called Edubuntu that sounds promising.

Edubuntu is a version of the Ubuntu operating system suitable for classroom use. As an educator you’ll be able to set up a computer lab, or establish an online learning environment, in an hour or less — then administer that environment without having to become a fully-fledged Linux geek.

I’m going to have to download the PowerPC Preview Release and play with it a little when I have a little a more free time for research. I can already think of a couple useful applications for some of the older iMacs in the building.