if ($('ad_slideshow')) {
  var ads = $$('#ad_slideshow a');
  $(ads[0]).show();
  setTimeout('showNextAd()',5000);
}
function showNextAd() {
  var ads = $$('#ad_slideshow a');
  var num = ads.length;
  for(var i=0;i<num;i++) {
    if (Element.visible(ads[i])) {
      Element.hide(ads[i])
      Element.show(ads[(i+1)%num])
      break
    }
  }
  setTimeout('showNextAd()',5000);
}