u cant. only in events
No. You can only get it from giveaways.
By Nintendo even or Pal Park
You have to trade it from a GBA game that has it.
Through an event.
You need to get the Pokemon Colleseum disk. Jirachi can be traded from Pokemon Channel.
No, it is inpossible to catch Jirachi on Diamon, Pearl or Platinum.
You can't catch Jirachi.
You must get Jirachi from an event in Diamond, Pearl, or Platinum then trade to heartgold. There was also a Wi-Fi event in which you could receive a Jirachi which has since passed.
Again, Jirachi is an EVENT Pokemon! (sorry for sudden rudeness, I've answered many stupid questions like this one -...-) There was a Jirachi event for Diamond and Pearl that once you traded it to HeartGold/SoulSilver, you unlocked the PokeWalker route, Night Sky's Edge
find it.
To catch JIRACHI you have to use the Pokemon colloseum disk. To catch DEOXYS you have to go to a Pokemon Nintendo promo event and get the aurura ticket downloaded on your game.
You can't catch Rotom in heartgold.