Instructions
Pause the game to load the sub-menu at the start of an exhibition match.
Scroll down to "Rosters" and press "X." Highlight the best dunk player on your team and go to "Edit."
Next to the "Package Dunk" selection, press "X" and select "Off." This will turn off their normal dunks and only load the specialty dunks. Press "Triangle" to return to the main menu.
Play the game. When your main dunk player has the ball, use the left analog stick to run him toward the hoop.
Hold "R2" down and when you are ready to shoot, press the right analog stick down. Your player will jump and do the specialty dunk.
Perform the specialty dunk controls at different points on the court to do different dunks. As you learn the different positions, you will figure out which dunks are performed where for all the different players.