var myUpdaterBannerA = null; 
var myUpdaterBannerB = null;
window.onload = function updater() { 
	var url = '/banners.php?zona=a'; 
	myUpdaterBannerA = new Ajax.PeriodicalUpdater('bannerA',url,{ frequency: 10}); 
	var url = '/banners.php?zona=b';
	myUpdaterBannerB = new Ajax.PeriodicalUpdater('bannerB',url,{ frequency: 10}); 
}