The menu you see here is done with a simple javascript that shows and hides layers. The menus are simply invisible page layers that are "unhidden" on mouseover. But there is a huge amount of work done here--each menu layer and sub-menu layer has to be exactly positioned. The page has to be static--not liquid design--and there is a CSS file that provides the rollover color changes, fonts, etc. Also, it weighs in at a whopping 54K in file size! This is what we usually aim for as the TOTAL page size.
View source for code.