Try adding a position and z-index property to your /css/screen.css stylesheet (at about line 68):
#outerWrapper #topNavigation {
background-image: url("../CSSMenuWriter/cssmw_images/menu_bg.jpg");
background-repeat: repeat-x;
height: 41px;
margin: 0;
padding: 0;
position: relative;
width: 950px;
z-index: 9999;
}