Check this link out. It is where I learned how to boot as many linux operating systems as I feel like and have it all bootable using grub.
Right now I can boot to SimplyMEPIS 3.3.1-1, 3.4.3, 6.0, 6.5 beta 7, knoppix and debian as well as a spare 6.5 beta 7 that I am going to upgrade to edgy using this link.
The post is by boemer. This way I can try anything that I want to 6.5 without wrecking my 'real' 6.5 beta as it is being built to the final using apt-notify and taking all of the recommended upgrades.
Just remember that when you are adding another linux be sure that it can install grub to root. Otherwise it may not work.