: I don't think it's too new; there's an OS 9 application in System
: Preferences, I just can't figure out how to use it. Also I want OS 9 to
: run old games other than Marathon.
It's impossible for you to boot up in os9, your computer is too new, but you can use os9 classic and it couldn't be easier to use it. double click on an os9 application you want to use and voila, the classic app starts up and allows you to run majority of os9 apps and games. :)
But for marathon i suggest http://source.bungie.org <- Aleph One for osx. At least after panther my original Marathon 2 and Inf stopped working (while the 1st one still works)