Instructions
Trade
Make a friend who has "Pokemon Emerald."
Start a new game and select one of the three starter Pokemon.
Play the game until you encounter another Pokemon. Use a Pokeball from the "Item" menu during battle to capture the Pokemon.
Go to the nearest Pokemon Center. Have your friend do the same. Save your games and restart the Gameboy. Connect the two Gameboys with the link cable.
Go upstairs in the Pokemon Center. Walk through the center door. Select your starter Pokemon to trade and have your friend give you a disposable Pokemon.
Save the game on both Gameboys. Have your friend store the first starter Pokemon. Repeat Steps 2 to 5, selecting another starter Pokemon.
Complete Steps 2 to 4, selecting the remaining starter Pokemon. Instead of trading the remaining starter Pokemon, have your friend send you the already-traded starter Pokemon. You will need to catch two Pokemon to exchange.