Windows SharePoint Services 3.0 provides new navigational elements that improve user awareness of the current context within a site or site collection. You can customize navigation through the user interface or programmatically to enhance the experience of users.
The following kinds of customizations in site navigation are possible:
Custom Navigation and New User Interface Elements
Customizing Quick Launch and the Top Link Bar Through the User Interface
How to: Share the Top Link Bar Between Sites
How to: Customize the Display of Quick Launch
Adding Links through the Object Model
Using a Custom Data Source for Navigation