By default login page should be displayed to all users
This can be done by specifying the security level of the portal to require authorized users
Only Admin users should see what is available right now .. Site, Groups, Site Editor and Dashbaord
Follow what I mentioned in my previous post about configuring this in the shared-layout.xml
Users should only see Dashboard Page with Dashboard Portlet...
Not sure how to do this properly. But if you specify the initial_uri in the login.jsp page, you can specify what page the user will be forwarded to when they login (although this is probably a bit of a hack)