Due to PPC technology you will be limited to either an old AIX version or some PPC Linux. I also remember NT4.0 had support for PPC, but I doubt you want that one
I don't know what your needs are but if it is Video stuff, maybe this is useful for you:
Ubuntu Studio - Wikipedia, the free encyclopedia
Also there is a faq for PPC related to Ubuntu etc., check the links:
http://ubuntuforums.org/showthread.php?t=427714