function subMenu(submenu) {
  var object = submenu;

  if(document.getElementById) {
    var element = document.getElementById(object);
    var argument = document.getElementById("menu_items").getElementsByTagName("DIV");

    if(element) {
      if(element.style.display == "none") {
        for(var i=0; i<argument.length; i++) {
          argument[i].style.display = "none";
        }

        element.style.display = "block";
      } else {
        element.style.display = "none";
      }
    }
  }
}