You can't.
trade pokemon
with action replay or by trading it
Arceas has to be caught in Pokemon diamond, pearl, or platinum, then traded to Soul-Silver and HeartGold.
Sadly, you can't get Arceus in HeartGold or SoulSilver. The only way to have it in HG/SS is to trade it from either Diamond, Pearl or Platinum.
You have to trade the arceus over from another game check out pokebomb.co.cc if you want to keep up to date with Pokemon info
I'm guessing you mean Arceus, and unless there's an event, you can't.
Celebi
There isn't a date for the Arceus Event in Pokemon HeartGold (unless you mean the event where you get Arceus). When you send over any Arceus into your HeartGold game, the event is activated. You'll have to go to the Ruins of Alph in order to do the event.
In Pokémon HeartGold and SoulSilver, Arceus is an event however bringing an event Arceus into the game will unlock something special in the game.
An event
Through an event.
Yep