Dan Wellman evaluates free and commercial software that can help you create menus that expand into sub-menus and are used as a means of navigating your site. He looks at browser-based and GUI-based formats and makes some recommendations.
The program is browser based, and very well documented; there are numerous help files including a step-by-step guide to using the software and the menu, and a host of examples to inspire you or help you troubleshoot. It is very easy to use and after playing around with it for just five minutes I had a web page with a basic two-dimensional navigation menu linking to other pages on it. What could be easier? My initial test menu fell far short of the limit of the capabilities that this program can offer you.