Between Mahogany Town and Lake of Rage.
There are a couple ways to get pikachu on Heartgold Soulsilver. one is with the wi-fi event for the pokewalker route "yellow forest". two, "Resort pokewalker route. three, "Rally" pokewalker route, and the "sightseeing" route.
You can't.
There is no such thing as mew three
Nothing happens after that. You just caught the three legendary roaming Pokemon in the Johto Region.
By Ruby I'm assuming you mean the Hoenn starters, then yes, you can get one of three of them in HeartGold/SoulSilver
pikhu bidoof
Trade them from HeartGold and SoulSilver.
nothing, you just have three legendary Pokemon
trade three pokemon from soulsilver to platnium its that simple talk to the people
You can't there are only three ways to get a lv100 train, trade, and migrate.
There are three Pokemon you can catch without a rod on Route 132 (by surfing): Tentacool, Pelipper and Wingull.
lugia, hooh, red garados but that doesnt really count, mewtwo, groudon, the three dog pokemon, the three bird pokemon, speacial event celebi,