[ic] Setting a promo code

[Bob Puff at NLE]

Hi gang,

I'm working on an old IC cart that uses a single checkout page.  This gathers all the user info, 
then processes the order.

I'm trying to wedge in a promo code routine that will give free freight if the code is correct.

My question: where do I put the code to test this condition?  After ord/checkout.html is submitted, 
what is the next file processed?  Obviously, I want this to affect what is stored to the database, 
as well as what is displayed, so I can't just put the code in the results.html file.

Thanks!

Bob