Things You'll Need
Instructions
Save your "Pokemon Ruby Version" game at a Pokemon Center with one empty slot in your party. Leave your Game Boy Advance on for the duration of this procedure.
Connect your Game Boy Advance to your GameCube with the link cable.
Boot up the "Pokemon Colosseum" bonus disc. You do not need the "Pokemon Colosseum" game for this method to work--just the bonus disc, which is still available on eBay for purchase.
Select "Special Gift Jirachi" from the bonus disc main menu. Jirachi will automatically transfer from the GameCube to the open slot in your party in Pokemon Ruby.
Disconnect the link cable after the Jirachi transfer is complete.