You can specify that only admins can see the portlets on the top of the page. You can edit the shared-layout.xml to specify which parts should be available to which users (gatein.ear/portal.war/WEB-INF/conf/portal/portal/sharedlayout.xml).
I am trying to figure out how you want the site to work. Are you wanting an unauthorized user to have to login, and then once logged in they only have access to the dashboard page? Or is there also going to be more to this than just a dashboard?