function ventanaSecundaria (URL){
   window.open(URL,"ventana1","width=500,height=400,scrollbars=NO")
}


function UpdateQty(cantidad,itemId)
{
	newQty=document.getElementById(cantidad).value;
	document.location.href ="mi_carrito.php?action=update_item&id="+itemId+"&qty="+newQty;
}


<!--
function MM_goToURL() { //v3.0
  var i, args=MM_goToURL.arguments; document.MM_returnValue = false;
  for (i=0; i<(args.length-1); i+=2) eval(args[i]+".location='"+args[i+1]+"'");
}
//-->