you can't transfer pokemon from black/white to diamond, it is impossible. If you mean to transfer from diamond to black/white, then you need 6 pokemon on diamond that do not know HMs, and they must be in tyour PC. Then on Black/White go to the transfer lab and talk to the scientist on the top floor. The DS will save, then you have to turn on your second DS (the one with diamond) and tap the ds download play icon. After this you will select the pokemon you wish to transfer, and then complete the minigame, after this it will verify that you want to transfer and then it will be done.