Reboot your Mac with the Linux media in your CD/DVD drive holding down the ‘C’ key as your Mac starts up. Now let’s go ahead and install Linux!
There are so many Linux distributions that covering the installation process of each is beyond the scope of this article. That being said one very important thing to keep in mind is the location of the bootloader. The bootloader must be located on the Linux partition and not the MBR (Master Boot Record). As an example, let's theorize that you have Mac OS X and rEFIt installed at this point. You use the partition Boot Camp created for windows as your Linux root partition, reformatting it to the Linux format of your choice and also creating a small Linux swap partition within that space. Your partitions would look like this:
Partition #1: rEFIt
Partition #2: Mac OS X
Partition #3: Linux Root
Partition #4: Linux Swap
In this case you will want to install the Linux Bootloader to /dev/sda3. This can be accomplished in a variety of ways depending on your choice of Linux distribution. OpenSUSE defaults to this location; however, other distributions may not. Be sure to look at your installation overview and ensure this is set properly before continuing.
At this point you simply need to finish your Linux installation and reboot. You will be greeted by the rEFIt boot screen and should have a fully functional Mac OS X/Linux dual boot machine!