Dratini can only learn Extreme Speed in HG / SS versions.
Go to the cave of dragons or whatever it may be called after beating the Gym Leader. There will be an old man in the center. He will begin to ask you a few questions. When you answer, "think about what the Pokemon would want", as the HG / SS guide book quotes. Depending on you're set of answers, the man will give you a Dratini, level 5. if you answered correctly, it will know the move