BootLocker

From Steven Eppler:

This is an access control security tool that will stop unauthorized users from accessing your system. It has many features that makes it easy to maintain a secure desktop. It allows more than one user to be allowed on your system, which prevents the sharing of passwords. It also allows more than one master account, while other utilities only provide one. Security settings are set quickly and easily. With the click of the mouse you can turn it off, turn on low, medium, high, higher, or maximum security. These different levels of security let you customize the application to fit your exact needs.