Hi,
I don't have an Esplora board, but from reading this;
The accelerometer is already on the board, looking at the arduino IDE in Examples there is under Esplora an example that puts the accelerometer output on the IDE monitor, you can start there to see the values you will need.
Tom.... 
PS I'm a bit puzzled, this is for a virtual pinball machine, why do you need joystick operation, I always thought the quickest way to get flipper operation would be the side buttons.