How can I load an older version of OSX onto my iMac?

Question

Hey:
I have a Mid-2011 iMac running 10.7 right now.  I partitioned the boot drive, creating a new space so I could load up 10.6 (in an effort to be able to play my older Diablo II and Warcraft games) but my retail CD version is not working.  I did some research, and found that this is because my hardware is incompatible with the oldest versions of 10.6.  What I am confused about, when reading through threads, is how can I  get around this?  Is there a way I can load up a newer version of 10.6 (like 10.6.3 or newer) onto this partition?  Do I need an older Mac to do this (right now both my laptop and iMac are running 10.7 but I could always borrow my Mom's laptop for a bit since she is running 10.6.x)?  Since I have a legal version of 10.6 I assume there is a way to do this, but I am not sure how to approach.  I'm pretty knowledgeable with computers & technology, so I just need a general outline to get me started.
Any help from the community would be wonderful.  Thanks so much in advance.

Answer 1

Thanks for the help, I appreciate it.  I'm not looking to replace my current operating system, because I primarily need to work out of 10.7.  I just need the older version (basically dual boot, choose which operating system I want at startup) to occassionally play the games that are not supported in 10.7.  Actually, I had heard of lots of people doing this but the responses were all over the place and I was hoping to get a concise thought of what will work for my specific scenario. 
Unfortunately borrowing my mother's computer is not  an option as she lives miles  from me and I would never know when I have the time or want to play.  Anyone who has played Diablo or Warcraft can sympathize, my mom would never see her computer again if I needed it to play these games. 
Thanks again.  I might try the external drive scenario, but was just hoping to be able to dual boot into 10.6 directly with the hard drive(s) in the computer because my USB and firewire ports are all taken with lots of other equipment (I'm a graphic/web designer so have 2 printers, wacom tablet, external backup, 2 large die cut machines and so much more already plugged in).  I'm pretty tapped out on ports without using a hub and I don't like the way they work (too many years in technology knowing that direct connect is the best way to go).