SITTING VOLLEYBALL has been part of the Summer Paralympics since 1980. At the London 2012 Paralympics, 110 men and 88 women will compete in two medal events at the ExCeL venue from August 30 through September 8. There are two classifications in Sitting Volleyball, disabled and minimal disability, with teams only allowed to have one minimally disabled player on the court at a time. There are two competitions, one for men and one for women. Both play on a court that is 10m long and 6m wide, but the height of the net varies, 1.15m high for men (about 3.75 feet) and 1.05m high for women (about 3.5 feet).
According to the description on the site of the 2012 London Summer Paralympics, "Sitting Volleyball is played by two teams of six. The object of the game is to land the ball in the opposition’s half of the court. The rules of Sitting Volleyball are very similar to its Olympic counterpart, however a part of an athlete’s body between the buttocks and the shoulder must be in contact with the court whenever a shot, or attempt at a shot, is made."
You can read more about Paralympic Sitting Volleyball on the site of the International Paralympic Committee.