The popup is not poping up

I installed the PopUp Promo <http://www.oscommerce.com/community/contributions%2c2281/category%2call/search%2cadvert>

Which file should I put this into. we use the osmax templates

Step 2: Edit the following file:

/catalog/index.php

Just before the </head> tag, add:

<?php
// RJW PopUp Promo v1.00 begin
if ($session_started == true) include('includes/popup_promo.js.php');
// RJW PopUp Promo v1.00 end
?>

can someone help?