function My_MM_showHideLayers() { 
  var obj,args=My_MM_showHideLayers.arguments;
  with(document)
  {
    if(getElementById && ((obj=getElementById(args[0]))!=null))
    {
        if(obj.style)
        {
            obj = obj.style;
        }
        obj.display=(obj.display=='')?'none':'';
        args[1].className=(obj.display=='')?'on':'';
    }
  }
}