To install Ubuntu 9.10 (Karmic Koala) is advisable to use ubuntu-9.10-alternate-powerpc.iso to download here
To install it booting from the LiveCD you need to burn it to a DVD, because the size of the iso-image is bigger than 700MB CD. If a CD-ROM does not support burning or reading from DVD, you can follow this thread to force iso-image to fit in a 700MB CD in MacOSX (but it should also possible in Linux using wodim with the option -overburn)
Here I describe a way to reduce the iso-image's size, just removing data (Kernel and Intrd) that are not needed for my architecture. When you mount the iso-image, you will notice that they are stored in /casper/powerpc (powerpc32) respectively in /casper/powerpc64.
Try it at your own risk!
Download ubuntu-9.10-desktop-powerpc.iso to the directory ~/Downloads (or wherever you prefer)
Checksum the downloaded iso-image
$ cd Downloads
$ wget http://cdimage.ubuntu.com/ports/releases/9.10/release/ubuntu-9.10-desktop-powerpc.iso
$ md5sum ubuntu-9.10-desktop-powerpc.iso
Download hfs.map to ~/Downloads. We'll need it to create a bootable powerpc iso-image
Mount the iso image
$ wget http://people.ubuntu.com/~cjwatson/hfs.map
$ sudo mount -o loop -t iso9660 ubuntu-9.10-desktop-powerpc.iso /mnt
Create a directory ~/custom-ubuntu (or whatever) where to copy ALL the content of the mounted CD
For PowerPC 32-Bit Users (G3 and G4)
$ cp -ra /mnt custom-ubuntu
For PowerPC 64-Bit Users (G5)
$ sudo rm custom-ubuntu/casper/powerpc64/initrd
$ sudo rm custom-ubuntu/casper/powerpc64/vmlinux
Generate an hybrid bootable iso-fs with genisoimage
$ sudo rm custom-ubuntu/casper/powerpc/initrd
$ sudo rm custom-ubuntu/casper/powerpc/vmlinux
(Do not forget to change '~' to your user name)
$ genisoimage -hfs -part -map /home/~/Downloads/hfs.map -no-desktop -hfs-volid "Ubuntu 9.10" -hfs-bless /home/~/custom-ubuntu/install -pad -l -r -J -v -V "Ubuntu 9.10" -o custom-ubuntu-9.10-desktop-powerpc.iso /home/~/custom-ubuntu
You should get in your /home/~ directory a new .iso image called 'custom-ubuntu-9.10-desktop-powerpc.iso' SMALLER than 700 MB. My image for ppc64 is 692 MB.
Burn the generated .iso image with your preferred application or with wodim
Unmount the downloaded .iso image
$ sudo wodim -sao custom-ubuntu-9.10-desktop-powerpc.iso
Reboot to check if it works as expected. As always, be patient when you boot a LiveCD, it can take longer than expected. At the yaboot prompt, hit TAB to see all possible options. Of course only those for your architecture are available. Choose live-nosplash-powerpc or live-nosplash-powerpc64 to see what happens when booting.
Please, don't forget that you can use the custom CD ONLY on the appropriate architecture (either ppc32 or ppc64).