Just an FYI. You can't down grade. If your Mac came loaded with Lion you can't install any OS below that which came with the laptop. I tried to reinstall my old OS  and was told that the install disk is no longer compatable with this computer.

I have now tried the load to an external HD angin the some problem. The computer wouldn't accept the old disk to load the OS. I also read online that all you had to do was to install Rosetta and the older progarms would work again. Nope. (Lion dose not support Rosetta.)  Sorry no going back.

Below is a website that list programs that are compatiible with Lion.

http://roaringapps.com/apps:table