Lock down a Mac for public use

Skerries

I have an old iMac which I acquired and I am going to set it up in our local community centre but I want to secure it as much as I can

I am not an Apple person so I don't know what is the best way to do this
I was going to install a browser content filter such as K9

What I really would like to do is install something like Deep Freeze but free but I can't seem to find anything

any ideas?

ED E

Old but a start maybe:
http://www.mac-forums.com/macos-apps-and-games/321959-osx-kiosk-mode.html