The 7th badge/gym is in Mahogany Town. The Gym Leader mainly has ice type pokemon.
You go to Sunyshore and challenge their gym.
Defeat the eighth gym leader.
Route 7, Cerulean Cave
beat 7 gyms
beat erika, fourth (celadon) gym leader, who uses grass Pokemon
Houndour can be found in Route 7 in SoulSilver and it can also be found in the Safari Zone.
They are rare in route 7 and the safari zone
no you can trade soulsilver pokemon to black
he is not in Pokemon soulsilver or Pokemon heartgold
POKEMON SOULSILVER come with a poke walker and the Soulsilver game
Pokemon soulsilver and Pokemon heartgold are basically the same game just different versions but i do recommend buying Pokemon soulsilver
In the Kanto region go on route 7 (night only)