If you are going to use Java (again, I don't encourage you to use it because many browsers have security problems running scripts), here are some applets that you can download from the Web.
Table of Contents (TOC) Applet. Uses a tree view interface (similar to Windows Explorer) for navigation. Because this is a concept of the operating system, users are already familiar with the control, and can navigate very easy and fast on your homepage.
Mindmap Applet. Uses a Mindmap technology for navigation. It is very intuitive and easy, and has multimedia extensions to make your site navigation something really special.