Step two: Create a bootable CD/DVD or USB flash drive. Step three: Boot that media on the destination system, then make a few decisions regarding the installation.

But how do you actually get it installed? Here, we'll show you how to create a live CD or USB drive, boot into Linux, and install it on your system.

Perhaps they referenced this guide to create a bootable Live USB on Windows, allowing them to test drive something like Ubuntu without making any changes to their PC.

His app automates the process of making a bootable install disk for both Lion and Mountain Lion—just run the app and let it do its thing.

If you want to boot into a live Linux environment but don't have a blank CD or thumb drive handy, you can actually boot right from your hard drive using GRUB and previously mentioned Unetbootin.

Finally, if you need to install Mountain Lion over Leopard—assuming you have the license to do so—a bootable install drive makes it easier to do so.