I'd step back and think out this some more. If you're selling products you will have a lot more than a single listing page to think about. You'll probably have a descriptive page for each product, the shopping cart page, the checkout page (or pages), a login page, an account area where order status can be tracked, and probably informational pages about shipping and refund policies too.
This may change the balance of your site. You can style Zen Cart to look however you want. So it is possible to use it only for the cart-related pages and style it to look like the rest of the site.
However, I've generally found it easier to bring the static content inside the Zen Cart and only worry about creating and maintaining one set of styling information.
Kuroi Web Design and Development | Twitter
(Questions answered in the forum only - so that any forum member can benefit - not by personal message)