function scroller () {
if (Window.getScrollTop()+600 <= $('banner').getStyle('height').toInt()){
$('skyscroll').effect('top',
{ onStart : clearInterval (prova),
  onComplete : prova = setInterval ("scroller()", 500)
}

  ).start(Window.getScrollTop());
}
}
window.addEvent ('load', function () {
  prova = setInterval ("scroller()", 500);
  }
  );