This post is for nVidia users who can't get the nouveau driver working. Early iMac G4 users typically seem to fall into this bracket. For more detailed information see here https://wiki.ubuntu.com/PowerPCFAQ#Troubleshooting .
These instructions are for 12.04 only.
1. Download an 'alternate' iso or 'mini' iso and install as normal. If you want to use a 'live/desktop' iso then you can follow or adapt the instructions in this http://ubuntuforums.org/showthread.p...8#post12336938 post.
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!
Linux nomodeset single
3. The best alternative to the nouveau driver is the nv driver. You can compile it yourself (there are instructions linked in the FAQ), or you can install a pre-compiled version:
4. Now you need to create an xorg.conf. This is a basic one:
wget -O /tmp/nv.deb http://ubuntuone.com/6QVpmfHCU3YmHlik7lred9
dpkg -i /tmp/nv.deb
The following will download the above file and move it into the right place for you:
Identifier "Configured Video Device"
Identifier "Configured Monitor"
Identifier "Default Screen"
Monitor "Configured Monitor"
Device "Configured Video Device"
5. Edit your yaboot.conf file to add the 'nomodeset' parameter permanently:
wget -O /etc/X11/xorg.conf http://ubuntuone.com/6loNPRkiKluH2ZOXt8HENV
Add 'nomodeset' at the end of the append line(s). For example:
Every parameter inside the quotes should be separated by a space. Save (ctrl+o) and exit (ctrl+x), then type the command
append="quiet splash nomodeset"
to copy the file across to the boot partition.
6. You can now reboot into a desktop:
Lots more information in the FAQ and Known Issues pages: