You also need to make sure that in Pokemon Channel you have unlocked the option to trade jirachi.
In Pokemon ruby/sapphire you need to have beaten the elite four and the champion and you need to have saved last in a Pokemon centre.
Link the GBA to the gamecube using the aforementioned cable and then turn on the GBA and the gamecube. With Pokemon channel wait for the main menu (don't load the game), go into options and jirachi will be one of them. The game's instruction booklet explains this much better
Hope I helped
You go to the space staion and walk up and talk to the guy in the white lab coat and once he say's number 100 he will ask you to go to space and there you will find jirachi
--EDIT--
Okay, Jirachi is very VERY hard to get but it's worth it.
All you need to do is catch every Pokemon in Hoenn! (that's 200, if you're counting). Note that they have to be CAUGHT, not just seen.
That includes legendaries (regi's, groudon & kyogre, lati's, etc.) and ALL GAME-SPECIFIC POKEMON! (ruby-only or sapphire-only). This means you will need both games and 2 gba's (or a friend with the other game and a gba) and a link cable.
Not sure about Emerald, but I believe the same works.
Please note me if I'm wrong, but I found this on several websites as ways to get Jirachi.
Pokémon in Pokémon Channel cannot be traded and no Pokémon from Channel can be transported to Pokémon Emerald. Jirachi is the only Pokémon capable of being sent over to a Gameboy Advanced game and only Pokémon Ruby and Pokémon Sapphire can receive it... in order to do it with either the Ruby or Sapphire Game Paks then you will need to start Channel, select Options then select Jirachi and then you'll see a cut scene of Jirachi arriving to visit Pikachu and then Professor Oak will ask if you want to transport Jirachi select "Yes" and then he'll remind you that the Ruby or Sapphire game that you're transferring to will need to be one that has beaten the Elite 4 and Steven and you'll need to confirm that it has and then he'll ask if your Gameboy Advanced game has a free place in its party so you'll need to confirm that it does and then you'll need the GameCube-to-Gameboy Advanced Link Cable (while making sure to connect the GameCube part of the Link Cable in the GameCube's 2nd Controller slot) and he'll ask if you're ready select "Yes" and then turn on your Gameboy Advanced and after about 10-20 seconds you'll have Jirachi downloaded into your Game Pak... Jirachi can only be unlocked in Channel once you've completed the main portion of the game and you can use either a Nintendo GameCube to help with transporting Jirachi or you can use the earlier Nintendo Wii models in place of the GameCube in order to assist with transporting Jirachi.
Use a link cable, Use the GBA to Gamecube one.
you can only get jirachi on Pokemon channel by an Nintendo event but you cant do it now so you will have to get a Pokemon collsseum bonus disc
This can't be done directly, but Pokemon from fire red and leaf green can be transferred to emerald, and from there they can be traded to ruby or sapphire.
You can't. You can only get jirachi in ruby and sapphire. You would have to trade from ruby or sapphire.
trade from ruby/Sapphire/emerald/firered/leafgreen. you can get them in these game bay special event, collosium bonus disc, or in Pokemon channel.
If you have the Pokemon Colosseum Bonus Disc for the Gamecube and Pokemon Ruby or Sapphire (and a special cable), you can download Jirachi onto one of those games and trade it to Emerald. I also hear you can get Jirachi on Pokemon Channel and send it to your games. Other than that, you have to cheat. :(
Umm....Gameshark Cheats,and trading. If its on Ruby and Sapphire,its on the Pokemon colloseum and Pokemon channel
there is 202 and you have to trade Pokemon and find them you were forgetting jirachi and deoxes
you have to have a us bonus disc of Pokemon collosseum trade it to ruby sapphire or emerald but if you have Pokemon diamond or pearl you will have to migrate.
just trade from someone else
In Pokemon Colosseum Bonus Disc, you can get Jirachi on ruby/sapphire/emeraldzperiodz Then you can trade Jirachi over to Leaf green/Fire red to do whatever you want with. ~M
You can't get jirachi in ruby unless you receive it from the Pokemon colosseum bonus disc.
sorry to disapoint you but there is no way you have to migrate it from your gba game i think on emerald Sapphire or ruby you can get it on Pokemon coloseum and Pokemon channel
What pokemon? jirachi
Currently, Jirachi is not obtainable through traditional methods in Pokemon Ruby Version.