For somebody with previous experience of sort of integration and knowledge of how the shopping cart is structured and managed in Zen Cart, it would be straightforward.
They'd write a custom handler to receive the XML data, parse it and populate the shopping cart, before directing the customer to the cart.
The customer would login or create an account and proceed through the checkout as normal.
When the order is confirmed as successful, the order id is passed to the checkout success page. this would be intercepted and used to read the order and provide the information back to the HLSM system, before taking the customer to the checkout success page (or redirecting them back to HLSM if that's more appropriate).
But there is a BIG caveat here. Although it's straightforward for the right person, somebody lacking relevant experience handling these sorts of feeds or sufficient Zen Cart knowledge will struggle and very possibly be unable to complete the task.




