Here’s a pretty good overview and how to on setting up Linux on a Mac or PC. I usually carry a few Ubuntu “live CDs” when I travel – these CDs allow you to boot in to Linux, but it won’t mess up anything on the hard drive. More often than not, the folks I show it to start using Ubuntu, it’s a pretty nice system and this how to is really handy to get it up and running on that old computer gathering dust you might have. Link.
HOW TO – Ubuntu Linux for novices