There was a post only yesterday about drop down menus as map positions:-
http://www.webdevforums.com/showthread.php?t=20858
Look at http://www.cssplay.co.uk/menus/flyout_wall.html
and CSSplay's main css file http://www.cssplay.co.uk/menus/css/fly_wall.css
which shows a fly-out menu positioned over a background. It is possible to adapt this to a horizontal menu by putting float:left in the li tags, plus a few other adjustments of course!
Code downloaded to my PC will be deleted in due course.
WIN7; IE9, Firefox, Opera, Chrome and Safari for Windows; screen resolution usually 1366*768.
Also IE6 on W98 with 800*600 and IE8 on Vista 1440*900.