I don't think BootCamp will allow you to install 2 Operating Systems. I believe you could partition the drive with Bootcamp, and then partition your remaining OSX drive. Then install a linux distro on the other partition.
I have not done so but I believe you can triple- or quad-boot your Mac, although BootCamp will not do so. If you have multiple drives or partition your drive, you can use a boot manager like ReFit to do so. I would search the forums for triple-booting and refit to see what you find. I am at work and don't have the time to look them up but I know there are posts on this topic.
