You have to trade the Pokemon you want to migrate to Pokemon Ruby, Sapphire, Emerald, FireRed, or LeafGreen. Then you can migrate using Nintendo DS or NDS Lite.
After you have the National Dex, you go down a hidden route off Sandgem Town, where you have to use surf. At the end of the route, there is this building called the Pal Park. You can migrate Pokemon...
First, you put in a Pokemon gba game (example:ruby, Sapphire, fire red, leafgreen, and emearld) then turn on your ds. Next, you chose migrate from fireredthen, it will show up a screen.chosse all 6...
you put your leafgreen in the bottom slot of the DS and your pearl in the top slot and go to the pearl starting screen amd it will say migrate from leafgreen choose the 6 Pokemon you want to migrate...