Yellow Dog linux is a very poor distro. It's repos are old, the default desktop is odd and hard to work with, and updates are infrequent. If I were you I'd stick to the standard distros like Debian or Gentoo. Many of the small distros that support ppc aren't very good. Ubuntu ppc is only available as a daily build of 10.10. So, unless you like using the stuff at the very very bleeding edge... It wouldn't be a good idea.
Basically, use Debian... or if you're daring use Gentoo.
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Yellow Dog linux is a very poor distro. It's repos are old, the default desktop is odd and hard to work with, and updates are infrequent. If I were you I'd stick to the standard distros like Debian or Gentoo. Many of the small distros that support ppc aren't very good. Ubuntu ppc is only available as a daily build of 10.10. So, unless you like using the stuff at the very very bleeding edge... It wouldn't be a good idea.
Basically, use Debian... or if you're daring use Gentoo.
List of ppc distros (most are outdated):
http://penguinppc.org/about/distributions.php