function build_menu() {
  var ul = document.getElementById("main_menu_top").getElementsByTagName("ul");

  for (var i = 0; i < ul.length; i++) {
    ul[i].parentNode.onmouseover = function() {
      this.getElementsByTagName("ul")[0].style.visibility = "visible";
    };
    ul[i].parentNode.onmouseout = function() {
      this.getElementsByTagName("ul")[0].style.visibility = "hidden";
    };

    ul[i].parentNode.onclick = function(e) {
      this.getElementsByTagName("ul")[0].style.visibility = "visible";
    };
  }
}

if (window.addEventListener) {
  window.addEventListener("load", build_menu, false);
}
else if (window.attachEvent) {
  window.attachEvent("onload", build_menu);
}