It's not too hard to install Ubuntu (just out with a new beta) on most computers. MacBooks, however, have a few unique quirks, especially if you want to keep OS X. FOSSwire has a thorough installation guide. Following along, you'll learn how to carve out space for Linux alongside your partition for OS X (and Windows, if you want to triple-boot), and use the rEFIt bootloader tool to create an easily-switch-able startup. You'll end up doing a little partition work, but it only requires the Ubuntu installation disc or USB drive you'd need anyways. This should work for the older line of non-unibody MacBooks, which have different hardware setups than the most current line. Found an easier way to get the orange-hued Linux distro on your sparkling white MacBook? Tell us how in the comments.