If you don't want to pay over 500 bucks for a super fancy navigation bar, packed with other tens of never-gonna-use controls, you can modify the below project.
What it does is take one accordion from ASP.Net Ajax Control Toolkit, and make it look like a navigation bar, in a custom control that derives from CompositeControl.
Styles are defined with CSS, you can add pictures to it, and many other things. In the end, the whole code is at disposal, and you can modify it as you think it's necessary for your application.
This is a proof of concept project. Download the VS 2008 C# project here:
If you like it and would like to use it, I would answer your comments and questions when my time allows me to.