function switchmenu(obj){
  if(document.getElementById){
  var el = document.getElementById(obj);
  var ar = document.getElementById("maindiv").getElementsByTagName("span");
    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";
    }
  }
}