function popup(url,ancho,alto){
	var ventana=window.open(url,'msgbox','width='+ancho+',height='+alto+',toolbar=no,scrollbars=yes,status=no');
	var left = (screen.width-ancho)/2;
	var top = (screen.height-alto)/2;
	ventana.moveTo(left, top);
	ventana.focus();
}