A PIN code is a personal invitation to reserve a Walt Disney World vacation, often offering a substantial discount on room-only or vacation package arrangements. They're usually time-limited to a specific set or sets of date, and can range from a simple room-only discount to a package discount which may or may not include a
free dining plan, discounted tickets or a combination of multiple discounts.
To even have a chance of getting one, make sure you're registered with the main WDW website, and have both provided a working email address and opted in to receive marketing and promotional offers. In my experience, anything you do on their website that indicates you might be interested in going to WDW will raise your profile in the system, which seems to improve the chances you'll be sent a PIN.
PINs are not transferable, but can usually be used within immediate families.
When booking with a PIN, you can either call or use the website (when it's working) and enter the 15-digit code to receive the discount/amenities associated with the PIN. There are always terms and conditions. Make sure you understand the offer and tailor your expectations accordingly.
Just be aware, you can register with the website, save multiple vacation offers for later, order the annual Vacation Planning DVD, and respond to every marketing email they send and still not receive a PIN. But none of that costs anything but the time it takes to fill in the forms and click on the links...
Good luck! Check the sticky for more information
http://www.disboards.com/showthread.php?t=1686236