http://pokewiids.wordpress.com/2006/08/03/emerald-cloning-glitch/
that's the cloning glitch. One thing though, there is a part in her method that makes the glitch much harder. From step 7 on, use this method:
The woman will tell you you must save the game. Select yes.
When it asks you if you would like to save the game, select no. After the save text goes away, turn off your game. This gives no chance for the game to eat your Pokemanz or save file. I used the method in the link, not that exact link but still the same method, and I lost a few pokes. Then I accidentally clicked no, and figuring that I screwed it up, I turned off the game. I turned it back on and the cloning had worked. So, anyways, there ya go.