Which Linux and which Mac? I would generally tend to install Linux on a PowerPC mac as GNU/Darwin makes Open Source tools available for more recent macs and you can get a nice X-Windows desktop without a whole new Operating system. I use slackware most of the time, which never supported the PowerPC and I'm not aware has specific Mac Support, but everyone else has and does. Here is Ubuntu's documentation:
https://help.ubuntu.com/community/MacBook
Here is a pretty good page about installing Fedora:
http://www.alphatek.info/2009/07/22/natively-run-fedora-11-on-an-intel-mac/
Slackware assumes you will take responsibility for your own maintenance:
http://www.linuxquestions.org/questions/linux-laptop-and-netbook-25/installing-slackware-and-mac-os-x-on-a-new-apple-laptop-690751/
I have my distro preferences but I like to remember that I am as opinionated and bull-headed as the next idiot. I therefore try to keep my answers as OS neutral as I can. Just remember, people have tried to install Linux on everything (warning, Satire):
http://strangehorizons.com/2004/20040405/badger.shtml
and they have written about it. You just choose your distribution and search for a tutorial about installing it on the Mac. I am SURE you will find it, with links to the exact iso file you want.