Have multiple navigation headers

Now that I have created by membership site I need a way to navigation the members only area.

How can I change the header/navigation on all of the protected pages.

Example: the main company website is purely information for potential clients.

The membership area is for salespeople to login and access company information. Once they login, the navigation needs to be able to change so that they can see all of the pages available to them.

Make sense? Any suggestions on how to accomplish this? Some of the options I have seen such as installing two copies of WP on the server seemed above my experience level.