Oh that sounds pretty cool, so as soon as an order is placed for a specific zip code, you want to fire off an email to the driver responsible for that zip code.
It sounds like you’re going to need a custom screen to store Driver Emails and the Zipcode(s) they deliver to and on the orders processing screen to automatically send that email.
I think the easiest spot for you to inject your additional code will be right after it sends the customer the email for the order that was place. Then add your logic to send an email to the driver based on the zip-code.
I’m basing this off my experience in osCommerence. I just to go here http://addons.oscommerce.com/ and pick a similar mod I was looking for and enhance it for my needs.