function switch_menu(obj){
 if(document.getElementById){
  var el = document.getElementById(obj);
  var ar = document.getElementById("mdiv").getElementsByTagName("ul");
  if(el.style.display != "block"){
   for (var i=0; i<ar.length; i++){
    if (ar[i].className=="submenu")
     ar[i].style.display = "none";
   }
   el.style.display = "block";
  } else {
   el.style.display = "none";
  }
 }
}