Black Jack Mini-Game
Beat the game, then, once the credits finish and 'The End' screen appears, press R2, L1, R2, R2, Up, X, Right, Circle, Down, Triangle, L2, R1, R2, L1, Square, Square. You will hear a sound to confirm you entered the code correctly. Finally, press Start to begin playing the Black Jack mini-game.
Submitted by TifaDC. 100% success rate. 

Go to: Final Fantasy 9 Info Page | nGaming Home Page.