how to in Javascript

I need help to figure out how to write a javascript code that will do what I want it too.
I am very new to javascript however I have been coding in php for while now. What I want to do is have a menu on my site that will drop down when the mouse is over it, and close when the mouse is not over it, I also want the menu to use an image with image rollover, but the sub-menus to be just regular text. I have put a picture of what I want on my sever to help make things more clear, you can see it at -> http://69.76.174.153/~spencer/random_img/sample.GIF <-

Thanks for any help you can give me.