Nintendo has announced how US players of Pokemon HeartGold and SoulSilver can access the Yellow Forest, a special Pikachu-themed route, on the Pokewalker. Players will have to connect to Nintendo Wi-Fi Connection from April 1st to 30th, download a Mystery Gift, and then acquire the route at any Pokemart in the game.
The Yellow Forest is filled with nothing but Pikachus, but some of them have unique capabilities. Some of the Pikachu naturally know Surf (like the special Surfing Pikachu in the past), while others found may actually know Fly.
The Pokewalker is the special pedometer/training device that comes with every copy of the recently-released Pokemon remakes. And yes, it is as addictive as the Tamagotchis of the past.