It has plenty of space on TWO hard drives. I think the possibilities are as follows.
1. Finally get an OSX 10.5 or 10.6 installation DVD and install that (unlikely, as I've failed so far)
2. Install MorphOS (I managed to boot from a DVD, so this proves it's compatible)
3. Install AmigaOS 4 (NOT 4.1) using an ISO file I downloaded tonight which says it uses the loader Moana and will install onto a Mac Mini G4. I don't know if my Power Mac G4 is compatible.
4. Install Yellow Dog Linux
5. Install Free BSD for Power PC
What do you think I should do with it and why?
Go for a dual boot system with MorphOS and OS X 10.4 or 10.5. OS X crawls and restricts you nearly everywhere in your freedom to do things as you like, but offers a few nice programs that are missing on MorphOS. I dual boot my Macs, ratio is probably about 95% MorphOS 5 % OS X.