Mac Savvy People: Possible to run two versions OS X on my Laptop?

Hey guys.
I have a quick question that one of you I am sure can help me out with. I would like to be able to run two versions of OS X on my macbook pro, the current 10.8 and either 10.5 or 10.6. The reason for this is several programs that I used before upgrading no longer work on my four year old computer running mountain lion. I know it is possible to partition part of my hardrive to run windows, but can this also be done for an earlier operating system the computer has already used? (It literrally hit me today that this might work, which would solve a years worth of frustrations...)
And if this is possible, is there a way to do it with out needing the operating system's installation disk?

Sorry if this is a "duh" question.. any help is greatly appreciated though!

 

Bump... Anyone?