if (document.layers) {
  visible = 'show';
  hidden = 'hide';
} else if (document.all) {
  visible = 'visible';
  hidden = 'hidden';
}

var lastmenu

function reveal(menu, parent) {
var daMenu;
  if (document.layers) {
    daMenu = document.layers[menu];
  } else if (document.all) {
    daMenu = document.all(menu).style;
  }
  
  if (lastmenu != null){
   if (lastmenu != daMenu){
     lastmenu.visibility = hidden;
   }
  }

  if (daMenu.visibility == visible) {
    daMenu.visibility = hidden;
  } else {
    daMenu.visibility = visible;
  }
  lastmenu = daMenu;
}