PowerPCDownloads
Since 7.04 Ubuntu, PowerPC downloads of Ubuntu are not available on all Ubuntu mirrors. They have been moved into the ports section of the main mirror.
Please review the PowerPC FAQ and the PowerPC Known Issues pages before installing. All the information you need for a successful install should be in those pages, so make sure you check them out first before wasting your time and effort on needless internet searches. Please do tell somebody on the Apple forum if you think the instructions are unclear or are missing something, but it would be great if you could make the improvement yourself!
Daily build of the current Ubuntu development release
At present, the current Ubuntu development release is 12.04 Precise Pangolin. The following iso's are available for testing. Please report bugs so that they get fixed prior to release.
Ubuntu
Alternate CD - http://cdimage.ubuntu.com/daily/current/
Lubuntu
Live CD - http://cdimage.ubuntu.com/lubuntu/daily-live/current/
Alternate CD - http://cdimage.ubuntu.com/lubuntu/daily/current/
Kubuntu
Live CD - http://cdimage.ubuntu.com/kubuntu/daily-live/current/
Alternate CD - http://cdimage.ubuntu.com/kubuntu/daily/current/
Netboot/Mini
11.04 Natty Narwhal and 11.10 Oneiric Ocelot
For 11.04 and 11.10 (Ubuntu, Kubuntu, Xubuntu, Lubuntu etc) use the mini CDs and follow instructions in the PowerPC FAQ.
10.10 Maverick Meerkat
Ubuntu
Desktop live install CD, alternate install CD
The Ubuntu Live CD image is above 700 MB when fully downloaded and cannot be burned onto a CD.
Kubuntu, Xubuntu, Lubuntu, etc
It is also possible to install by using the mini/alternate CDs and then installing either the kubuntu-desktop, lubuntu-desktop, or xubuntu-desktop packages. See instructions in the PowerPC FAQ.
10.04 Lucid Lynx LTS
Ubuntu
Desktop live install CD, server install CD, alternate install CD, and netbook live install image for various platforms
Kubuntu, Xubuntu, Lubuntu etc
Kubuntu http://cdimage.ubuntu.com/kubuntu/ports/releases/lucid/release/
Xubuntu http://cdimage.ubuntu.com/xubuntu/ports/releases/lucid/release/
It is also possible to install by using the mini/alternate CDs and then installing either the kubuntu-desktop, lubuntu-desktop, or xubuntu-desktop packages. See instructions in the PowerPC FAQ.
8.04 Hardy Heron LTS
Ubuntu
Desktop (Live cd), Alternate (text mode installer), and server cd:
Kubuntu, Edubuntu
Kubuntu http://cdimage.ubuntu.com/kubuntu/ports/releases/hardy/release/
Edubuntu http://cdimage.ubuntu.com/edubuntu/ports/releases/hardy/release/
Old Releases
Mirrors
This is not an exhaustive list. Using the list of official CD mirrors and a bit of ingenuity traversing the directory strcuture (for example, click on the Parent directory/ or ../ link) you can probably find more mirrors that contain ports releases.
Academic Computer Club, Umeå University, Sweden
Silicon Hill, Czech Republic
University of Waterloo Computer Science Club, Canada
LeaseWeb, United States
Technische Universität Dresden, Germany
Internode, Australia