You can use the procedure below, but be aware that anything on the hard drive will be gone, which it sounds like it is already anyway. You will need the Snow Leopard disc to do it though.

http://gigaom.com/2011/07/26/how-to-downgrade-from-lion-to-snow-leopard/

IMO you should just put Lion back on and find replacements for the apps that won't work.