Setting up tracking for your offer is fairly straight forward if your site is using Zen Cart.

Zen Card provide a great guide which you can see here:
http://www.zen-cart.com/content.php?299

The only variable you will need to include in the tracking code is the order total (without currency). The amount you pass to us must be in GBP. So you store needs to be in GBP, or you need to have some way of converting the amount before you pass it back to us.