Bartik theme main menu
Take a look at the module Nice Menus or Superfish menus.  Both offer a lot of flexiblity and control for managing menus.  In both cases you will configure the module to provide some menu blocks and configure the blocks to attach them to your main menu.  You will then put the Nice Menu (or Superfish) block where you want it and hide the main menu block.  (I like superfish)