There are several ways to maintain an original GRUB config and add other OSs, either permanent or temporarily. In the following link, and on Herman's entire "page", you can see various ways. I usually chainload other distros, as many as one wants. http://members.iinet.net.au/~herman546/p15.html
There is an example in there (you'll have to prowl) of someone who loaded more than 100 OSs by chainload method.
The key is to never, never, never
let an installer do its thing automatically - always interrupt and put GRUB where you want it. I find it helpful to keep a written listing of partitions, etc. but the list is usually out of date. You could keep a printout of GRUB menu.lst.if you have a large number of OS installations.
I might also point out that it is very helpful to understand exactly the video arrangement your system has so that an install does not break it. Particularly with ATI, the newest proprietary driver/Cata;lyst drivers will break with older non-supported cards.
"Books? Who needs books? They don't taste all that good." The American Connoisseur, circa 2010
"Radiation is good for you.Everyone should eat radiation to be fulfilled. (free translation)...Ann Coulter, circa 2011