I received a code from my Disney Visa informing me of the free dining promo. As others have said, you have to book the room at rack rate and get MYW tickets. The code was released around June (I don't remember completely) and you had so many weeks to call and book your trip.
Edit:
I believe (I'm not positive) that if you come across a discount code and you already booked your trip, you can call and add the code to your trip (assuming its the same time).