The following user roles are predefined in the code base of the customer portal product:

Super
Billing
Order
Service

By using these specific roles you can control what functionality a logged in user will have access to when using your installation of the customer portal. There is a UDF on the Business partner contact person record in B1 that is called V33_ B1WebRoles that should be populated with one of these choices.

Here is the breakdown of what pages each role has access to:

Super = can view all of the pages in the customer portal
Billing = can view the statement and pay online pages
Order = can view the "your orders" and "your quotes" pages.
Service = can view the "new service call", "open service calls", and "closed service calls" pages

Once you update that information in B1 and save the information the customer portal will use these roles to hide the required pages.