The reason for orders not appearing in your admin area ... is that PayPal's server hasn't notified you that the order is completed. PayPal has to talk directly to your website to alert the order and "release" it so that it's viewable in the admin and sends out the order-confirmation emails, etc.

That's clearly not happening. It could be a result of the Zen Cart software version you're using, or it could be a problem with how you've configured the PayPal IPN module's settings in the admin, or perhaps a currency mismatch issue, or more.
Detailed troubleshooting and explanations are available in this article:
http://www.zen-cart.com/wiki/index.php/PayPal