Aimee, in the past, this promotion has come out about tax time (mid April) and had normally applied to August through end of September. They used to advertise on TV but as the parks are getting more crowded and as they normally offer the deal to foreigners first, they may not need to do that. It will be listed on the Disney website under specials. Also, it will be all over the internet.
You do not have to book through Disney. You can book AAA, other travel agents or Disney directly. Same payment applies to all as people have listed.
I will tell you as a family of 4, this package has been huge. If you were to eat like you do with this plan, you'd pay at least $1000. or more than the booked rate. You can always look at pricing of what full rate magic your way package with dining. Then recalculate taking out the dining. It is eyeopening. We certainly could go cheaper off site only eating counter services etc. But this free dining allows you to have counter and sit downs plus snacks. It has allowed us to try almost all the restaurants and really enjoy the experience. I would highly recommend it. I would also recommend that you book now at a moderate resort for the dates you are looking at. When the deal comes out, you can switch the reservations. Why is that important? You have to get your dining reservations in so you will not be left high and dry or eating at 9 pm because all of we who already have booked free dining (we booked before we left last year) have already made reservations. Good luck.