A Mac that old didn't ship with Mac OS X 10.4 on it.
According to the Peppermint Linux page it requires an x86 processor. Your Mac is PowerPC. (
http://peppermintos.com/about-peppermint/ - I'd never heard of it until now) So you need a Linux distro that's built for PowerPC. This rather limits your choice.
You could look at Yellowdog, or Ubuntu has a community supported PowerPC version.
http://ubuntuforums.org/forumdisplay.php?f=328
Note that you can't get Adobe Flash for PowerPC Linux. If you want Adobe Flash you'll have to stick with Mac OS X 10.4. That version of OS X is no longer supported by Apple though. You can run Firefox 3.6 and Adobe Flash on it though. (Mozilla will drop support for Firefox 3.6 before the end of the year.) There's only one newer version of OS X that will run on PowerPC, 10.5, and that requires at least an 800Mhz processor.
To be honest such a Mac is a bit of a relic. The sort of machine that are really only of use/interest to enthusiasts who understand what they're dealing with and are willing to make the effort to make them useful. Check how much memory it has and compare that to stated system requirements of any version of Linux you're considering installing. If it's 128MB or less that will limit your choice of distro even more and you might want to consider upgrading it. The thing is the type of memory it uses is utterly obsolete and buying new will be surprisingly expensive compared say DDR3 which is what pretty much everything uses theses days. Second hand would be the way to go.
