Superfish Horizontal Category Topbar Menu, JQuery and/or CSS.
Install a horizontal category CSS drop-down menu in the header. The menu functions exactly as the menu in the categories box, except horizontal.
The menu will function in pure CSS or with smooth JQuery functioning.
Links to demos at www.niora.com/css-oscommerce.
Category Box as Nested Unordered List for EZ(er) CSS & Dynamic menus v
Superfish Jquery Menu plugin http://users.tpg.com.au/j_birch/plugins/superfish/#examples