All you have to do is go to guest services at any of the parks when you get there. If you have an AP, they can look you up in the system, but if you are going to purchase the DVC TIW card, you will need your DVC membership card. It only takes a few minutes for the transaction, so I am not sure ordering the card ahead of time is necessary, unless you have a table service meal planned before you will be at a park.
Don't forget to take your picture id, too. We don't carry ours in the parks generally, and DH had to run back to our room at BWV to get his id so we could purchase TIW. Nothing like a little extra exercise on day 1....