parental controls on 10.5? How

I am trying to set up parental controls on my OS 10.5 operating system, on a Mac I have owned for quite a few years. I set up my own account name when first bought the computer. I want to make sure that my computer cannot be used by anyone else. How do I go about doing that? (I made another account name today because my computer said I had to make another account name, that I could not make the administrator name into the account name using parental control. I didn't do anything with the new account name because the instructions on the screen got to confusing.) Noah