Don't use this, just save yourself endless headaches and use WooCommerce. I use both WooCommerce and WP e-commerce and the only site that gives me trouble is the WP e-commerce site. My customer has been unable to receive payments now for a month due to a bug, yet nothing changed on the server or at the payment gateway. I've lost days now to trying to find the issue with no success and I'm reaching the point where I'm thinking it'd be quicker and easier to just port this site to WooCommerce.
Seriously, just don't waste your time.