Password Protecting FrontPage Webs

I setup a IIS 5.0 web server running FrontPage Server Extensions. How can I set it up so that, when a user has FrontPage open and tries to open my root web and subwebs using an http protocol, i.e. http://mycompany.com/subfolder it will prompt for them for their domain user name & password? I want it to work without causing any problems when trying to access http://mycompany.com/subfolder using their IE browser. I have my root web/subwebs stored in c:\inetpub\wwwroot folder.