Yea evil_tak
but are you sure that debian supports PowerPC ??
I don't know but i'm sure it doesn't support Power PC.
Umm a good distro for Mac would be yellow dog, its a Power PC version of Red hat, but I'm not sure that your old Mac is going to be able to run it though, go to
www.yellowdog.com and check it out!
By the way if you don't know what i meant by Power PC, its a particular Processor that Mac uses. Like Pc with intel and AMD.