function auf(menu) 
{
  if (document.getElementById) 
  {document.getElementById(menu).style.visibility="visible";}

  // ie5
  if (document.all) 
  {document.all[menu].style.visibility="visible";}

  // nn4
  if (document.layers) 
  {document.layers[menu].visibility="visible";}
}

function zu(menu) 
{
  if (document.getElementById) 
  {document.getElementById(menu).style.visibility="hidden";}

  if (document.all) 
  {document.all[menu].style.visibility="hidden";}

  if (document.layers) 
  {document.layers[menu].visibility="hidden";}
}