you will need to have user level authentication for this:
http://assets.webassist.com/solutionrecipes/securityassist_user_level_auth_sr.pdf
set the registration page to have admin access and the other pages to have standard access.
Your friends over here at WebAssist! These Dreamweaver extensions will assist you in building unlimited, custom websites.
These out-of-the-box solutions provide you proven, tested applications that can be up and running now. Build a store, a gallery, or a web-based email solution.