Hi - I spent a bunch of time to get my stock g4 cube with 15" studio display and ATI Rage 128 Pro video card running Ubuntu 8.04. So ... here are the steps I took to get the standard LiveCD (ubuntu-8.04-desktop-powerpc.iso) up and running. Perhaps this will be helpful to somebody else.
Boot the computer holding down the "c" key with the Ubuntu LiveCD in the drive. At the boot prompt, type:
Wait awhile ... eventually you will have a black screen after the gnome display manager tries to load. Type ctrl-option-f1 to get to a prompt, then type:
sudo killall gdm
This will stop gnome from loading. Next we need to edit the xorg.conf file. This thread - http://ubuntuforums.org/showthread.php?t=772808 - had the settings that work for me. Using nano or your favorite text editor, do the following:
sudo nano /etc/X11/xorg.conf
In the Monitor section you'll need to add the Horizsync and Vertrefresh:
Identifier "Configured Monitor"
In the Screen section add a Display subsection:
Identifier "Default Screen"
Monitor "Configured Monitor"
Device "Configured Video Device"
At the end of the file, add the following:
Save your changes and exit (ctrl-x in nano). Type:
sudo /etc/init.d/gdm start
If all goes well, gnome loads and you are on your way. I did an install to the G4 Cube hard drive, which went well. After rebooting, everything loaded up just fine with no user intervention (cheer). Trying to do updates, the updater crashed once, but after rebooting, I was able to finish all updates. I set this up hoping I could get MythTV backend up and running, but seems like many myth components do not yet have ppc packages. Oh well...
A couple things to note:
Sound might not be working ... I don't have speakers plugged in but my volume control has an "X" through it.
The standard airport card does not support WPA in Ubuntu - there may be a workaround but none of them appear to be very simple - I'm just plugged in via ethernet for now.