"Licensing" of Already Delivered Software?

Matterama asks: "My partner and I are treading on thin ice. We delivered six microprocessor controllers with source code libraries to a customer, under a written agreement to negotiate the license for that code from us once they got it working with their system. That time is upon us, and we realize that we do not know how to go about this (yep, we're pathetic). They want to buy 1000 units, and we are not setup to be a Microsoft (nor do we want to be). If I'm going to get a good, simple answer that puts money in our pockets for our work, it will be here. Can Slashdot recommend solutions or sites with solutions?"