Instructions
Take your virtual puppy for a walk. Every time you go for a walk, there is a chance to find a present with a "Fireman's Hat" or "Jack Russell Book" inside. These items will unlock two of the hidden breeds: Dalmatian and Jack Russell Terrier.
Play "Bark Mode" with a friend who owns another version of Nintendogs. Have your friend select a breed not available in your game, and meet them in-game using the Nintendo DS' wireless connection. This will unlock your friend's breed of dog in your game and vice versa.
Win championships to earn "Trainer Points." The more Trainer Points you earn, the more breeds you unlock. In order to unlock all breeds in your game version, you will need to accumulate 50,000 Trainer Points.