Firstly, many thanks to all of you who can give me a better solution:-)
My requirements are:
1. Two levels navigation.
2. The second level should be always displayed.
3. The active menu (both of the first and second level's menu) can be highlighted.
4. After the mouse is moved out the navigation bar, the menu bar can automatically switch back to the actived menu bar.
I want to create a navigation bar like: http://cn.wsj.com/gb/index.asp
But my navigation bar can not display the second level if I move away my mouse----the second menu bar will be disappeared.
So my question is:
How to create a two levels horizontal navigation bar and the second level is always displayed.