function preload()
{
    menu_on = new Image();
    menu_on.src = "/img_all/pfeil_on.gif";
    menu_off = new Image();
    menu_off.src = "/img_all/pfeil_off.gif";
}

function on(name)
  {
   document.images['navi'+name].src = menu_on.src;
  }

function off(name)
  {
   document.images['navi'+name].src = menu_off.src;
  }