navMenu = function() {
                if (document.all && document.getElementById) {
                                var topnavmenu = document.getElementById('topnav')
                                if (topnavmenu) {
                                                var submenus = topnavmenu.getElementsByTagName('UL')
                                                for (var i=0; i < submenus.length; i++) {
                                                                var mouseEvent = submenus[i].parentNode;
                                                                mouseEvent.onmouseover = function() { this.lastChild.style.display = 'block'; }
                                                                mouseEvent.onmouseout  = function() { this.lastChild.style.display = 'none';  }
                                                }
                                }                              
                }
}
navMenu();