How can I "Factory Reset" my mid 2006 iMac

Hello,

So my school was throwing out computers and they gave me this Mid 06' iMac with Snow Leopard (1.6.8). I wanted to reset the computer to factory settings, but when i tried to enter recovery mode It wouldn't come up. I don't have the disc for the OS X, but I can get them soon. I just want to know if there is a way to reset this computer, and if it has anything to do with being owned by a school, and if there is some program stopping me from reseting it, and how to get rid of said hypothetical program.

Much thanks,

Evander.