I've got a few iMac G5's hanging around gathering dust and I'm going to sprooch them up and load Ubuntu with Java JDK and BlueJay to be used as programming stations.
DOWNLOAD UBUNTU PowerPC
Get Ubuntu from here:
I've gone with the Ubuntu 12.04-alternative ISO http://cdimage.ubuntu.com/releases/12.04.2/release/
STEPS
1. Boot iMac holding down C
2. Followed installation instructions
3. Had a problem connecting to DHCP for IP Address allocation so I've just allocated a static IP Address
4. Installation ran fine until it got to the "Install" part and it just failed with "Install the System: Installation step failed" no further explanation..
So I downloaded MintPPC and I've just finished loading it... worked a charm!