I warmly recommended either xubuntu or lubuntu, given that you are at v11.10 together with the age of your PC.
Looking at packages.ubuntu.com, no PowerPC packages are described either for the xubuntu-desktop or lubuntu-desktop metapackages. They have been subsequently released - details of 11.10 PowerPC packages can be found on LaunchPad.net - for example the xubuntu-desktop package.
Since these meta packages have been now pushed into the standard repositories you can install the xubuntu & lubuntu desktops via
sudo apt-get install xubuntu-desktop
sudo apt-get install lubuntu-desktop
Looking forward, it appears there will be a PowerPC ISO available for Lubuntu. At the time of writing there doesnt appear to be an equivalent xubuntu PowerPC daily build though although this may change. Please consult the PowerPC FAQ for more details.
If you want to give the daily build a test, remember to image your partitions first as per the
dd answer as per the linked question. Do remember, this is alpha quality software.
- How to make a disk image and restore from it later?