Securing the Desktop from Physical Access

Securing the Desktop from Physical Access.

We have a group of computers in a public area that have access to some internal network resources. Think of it as a Library.

I am looking for way to make sure access to the desktop is not possible by someone other than the user. Currently I only idea I have to recommend is that the automatic screen lock be turned on after 5 minutes or so of inactivity.

Any recommendations are welcome.