function toggle_menu(nr)
{
  if (document.layers)
  {
    current = (document.layers[nr].display == 'none') ? 'block' : 'none';
    document.layers[nr].display = current;
  }
  else if (document.all)
  {
    current = (document.all[nr].style.display == 'none') ? 'block' : 'none';
    document.all[nr].style.display = current;
  }
  else if (document.getElementById)
  {
    vista = (document.getElementById(nr).style.display == 'none') ? 'block' : 'none';
    document.getElementById(nr).style.display = vista;
  }
}