Advanced security features??

Here's my problem, need solution...

My 27" Imac is main computer and the only one I have in the house,
Due to a lot of customization, it can be screwed up easily.
Things like 4 different operating systems to boot from, 2 boot camp partitions, GPU overclocked, very custom cooling software for windows, etc etc etc... Theres a lot of things that can be messed up by an ill-timed restart, or running a game without turning the cooling on, or x-ing out ofg my OCing software etc etc etc..

I set the computer up so that there is a 10GB partition copy of MAC OS 10.6
I have lots of guests and I want to just leave this up for guests to use.
I want to SECURE it!
Things like locking restart, no downloading files, no access to other drives, lock certain programs, stuff like that.

MY QUESTION>
Is there a way in the OS or an APP that I can do this stuff with?
Doesnt have to be free
THANKS!

OS X supports a Guest account that will do what you want. You can use Parental Controls to really limit the applications that the Guest account can use. But all files created by the account are deleted when they log out and so on..

hmmm that sounds good. I'll try that. thanks