Try this thread click here for a couple of possibilities to start out with.
FrontPage also has a subweb feature, where you can run a website within a website, and you can give user access permissions to the subweb. Try this link click here for some general information on subwebs.
A full log-in system for user authentication is always most secure, but you need server-side scripting support (PHP or ASP are the most common) and a database is almost completely necessary, although there are some solutions using plain text files.
The Spooky Login suite is a possile start for you:
If you browse the Hotscripts.com click here site there are loads of alternatives in all the mianstream dynamic languages for user authentication and password protection, many of which are free.
That should kick you off to a start at least.