First of all the menu items must be there, so you'll have to change how the main menu is rendered on the server side. Maybe you can do it with a PageTree control instead of the PageList which it probably uses OOTB.
Removed: Accidental double-post.
I've been playing around with the AlloyTech template. You'll notice that the main menu has no drop down submenu.
What would I need to do so that a sub menu would appear below when you hover on each main menu?