Is it possible to only show posts in the admin section for the logged in user unless they are an admin?

I have a real problem with anyone being able to edit/delete something I or another member posted.

Does anyone know where this is called from in the program? Like what .php page I would look to see if I can customize this?

Thanks
Broc

Or, instead of allowing people to register to post, can it be set to only allow registered users to comment?