This post is for users struggling to get Ubuntu/Lubuntu/Xubuntu/Kubuntu working with an iMac G3. For more detailed information see here https://wiki.ubuntu.com/PowerPCFAQ#Troubleshooting .
1. Download an 'alternate' iso or 'mini' iso and install as normal.
2. After installation, make sure you have an ethernet cable connected and boot into single user mode. So at the yaboot prompt type:
This will boot you into a root prompt so be careful what you type next!
3. If you have used a 12.04 alternate iso then you need to update the kernel:
4. Now you need to create an xorg.conf. This is a basic one:
apt-get install linux-image-powerpc-smp
The following will download the above file and move it into the right place for you:
Identifier "Configured Video Device"
Option "ForcePCIMode" "True"
Identifier "Configured Monitor"
Identifier "Default Screen"
Monitor "Configured Monitor"
Device "Configured Video Device"
5. You can now reboot into a desktop:
wget -O /etc/X11/xorg.conf http://ubuntuone.com/0npbpgYS6r521c5YAIoxMn
6. If you are using 12.04 then you can download the mesa legacy package to give you 3D acceleration. You can find a pre-compiled version here http://ubuntuone.com/379TLoe7yo2IAiOijAsOjQ
Lots more information in the FAQ and Known Issues pages: