What dates are you planning...
free dining (general public) usually runs starting the Sunday of the week before labor day. This year, that would be starting on August 23rd. We went for the start of free dining last year, flew down on Saturday with a room only 1 night, and started free dining on Sunday. Free dining means you get the basic
DDP free (1 snack, 1 Quick Service, 1 table service meal per day per person in your room). For most people, this is the best discount you can get. However, if you are a party of 2 (or even 2 adults with children under 9) and are staying in deluxe resorts, other discounts may be better. Free dining *usually* opens up for sale to the general public sometime in April. If you have a Disney Visa, you can usually book 3 days before the general public.
PIN codes - these are generally referring to special offers that Disney sends to your e-mail. Hard to tell how to get on that list. Usually it is 20 % to 40 % off room rates.
Public codes - These are codes open to the general public, free dining is one of these codes. They are typically listed on Mousesavers (History of codes is available here
http://www.mousesavers.com/historicalwdwdiscounts.html )
Right now, there is a public offer through August 15th for stay 4 nights, get 3 nights free. If you are going for 7 nights, it's a near unbeatable deal. There will likely be more deals coming past that date as the economy continues to go into the toilet.
SkierPete