No, you cannot trade from Gen IV to Gen V.
Gen IV (HG/SS/D/P/Platinum
Gen V (White/Black)
If you want to get your Pokemon from Gen IV to Gen V then you must first complete the main story and continue on to the PokeTransfer where you will need two DS/DSi/DSi XL/ 3DS and you can trade via that way by trying to catch the Pokemon you chose in a minigame.
PokeTransfer is on Route 15. I believe it should be the left route of Black City/White Forest.