Once on the Hempstead Turnpike, and you pass Nassau Coliseum, TURN OFF YOUR GPS, and LOSE YOUR MAPQUEST DIRECTIONS.  For the South Side field, make a left on Uniondale Avenue, and then a right into the field entrance as shown above.  Parking is in front (south of) the Stadium.  For the North Side fields, make a right when you see the Dunkin Donuts on the left.

You can drive from the North Side to the South Side, or it is about a 5 - 10 minute walk.