Hi Belinda,
Triple booting is pretty easy but you just need to know a few limitations. Due to MBR (master book record) limitations you can only have three partitions, which means that you can't have a swap partition (which generally linux distros do). So what you normally do is make a swap file after you've installed linux.
When you actually install linux you want to install the boot manager (which is usually grub) on the actual linux partition (not over the MBR). Then install rEFt (
refit.sourceforge.net/) which is basically just a OS selector (allows you to choose which OS to boot into when you start you're mac - has neat graphics too).
Other than that you don't need any special software, just disk utility. Basically just use disk utility to change (can resize any HFS+ partitions and can also remove other partitions without killing data on the HFS+ partition) to make 3 partitions (usually format the other two as MS-DOS - the windows and linux installers can change them to whatever).
If you can post a screenshot of disk utility's partition tab (I'll post a picture of mine) then I can see what's best to do.
Jay.
