Secure Login Section!

Hello,

I am about to start creating a website for a client and will need a login section for registered users where they will see a different menu bar or extra menu bars / Hidden content. eg

Non Registered members will only see:

Home | About | Contact Us | Login / Register

Registered users will see:
Home | About | Contact Us | Buy Products | Logout |

The Login section has to be viewable by all and on the front-end of the website. Once logged in they will see the extra menu on the top or a menu that I will create on the sidebar.

Anyone got any Ideas if there is a plugin or anything?

Thanks

Justin