gmc,

What, the menu drops down behind the slider images, right? If you'll look in your includes/templates/your_template/css/stylesheet_header_menu.css for any entries of "z-index: 1000" and change the number to a higher value than 1000, that should do the trick.
But, of course, if you had a url, and we could SEE the site, we could help you with a more EXACT solution..........:)