var current_submenu = -1;


function toggle_submenu(id){
  // we extract the menu number from the id passed in
  // and then display that sub menu in the designated box.
  var obj 
  if (current_submenu > 0){
    obj = document.getElementById("submenu_"+current_submenu);
    if (obj != null){
      obj.style.display = "none";
      current_submenu = -1;
    }
  }
  
  obj = document.getElementById("submenu_"+id);
  if (obj != null){
    obj.style.display = "block";
    current_submenu = id;
  }
  return false;
}