Rollover menus Help!!

Hi all

 I've seen this page http://www.rapidshare.com
and they have exactly the
type 
of navigation on the main menus at the top, I thought of for my website.
Does 
anyone know how to do it, I mean the code. 
 I've copied the code and paste it on a new do***ent in Dreamweaver but it

doesn't work. I think it might be a javascript or something.
 Any help will be very much appreciated.

 Take care.

 Z.