Use Secure Virtual Memory

An introduction into the Security Pane - Make your computer more security

How to Open the System Preferences in Mac OS X Leopard

IF you want to lock the computer, you can enable a menu bar icon allowing you to do so

Stop your computer from automatically logging in to an account

Disable the Apple Remote Control from having an effect on your computer

Enable the Security Vault - encrypt your personal data

Change the Master Password for the Security Vault

Turn off the File Vault

Have your computer log out after a specified time of inactivity

Password protect the System Preferences, stop people from changing setting without an Administrator account

Password protect your system using a password protected screen saver