When you connect the Pokewalker to a different game it reset everything (I had to reset mine before when I restarted Soul Silver), so you will not get any Pokemon or items that are on it.
Also how to connect to a different game: From the main menu select "Connect to pokewalker" you'll see "Save, then go for a stroll" , hold the down button on the thing that looks like a + and X, then press "L" once you've read "Caution" press YES you'll see the screen to the right, and the pokewalker will connect to the DS system (this is the Yahoo answer if you look it up).