var tot_banners = 4;
				var now = new Date()
				var sec = now.getSeconds()
				var ad = sec % tot_banners;
				ad +=1;
				if (ad==1) {
				banner="imagenes/mano.jpg";
				width="259";
				height="257";
				}
				if (ad==2) {
				banner="imagenes/biblioteca.jpg";
				width="259";
				height="257";
				}
				if (ad==3) {
				banner="imagenes/martillo.jpg";
				width="259";
				height="257";
				}
				if (ad==4) {
				banner="imagenes/libroma.jpg";
				width="259";
				height="257";
				}
document.write('<img src=\"' + banner + '\" width=\"' + width + '" height=\"' + height + '" border=0>')