What doesn't work as expected? The direction, the bullet selection? Anyway, I would add rigidibodies to the bullet prefabs, and define the prefabs in an array in the Inspector. To define the spawning position/rotation and direction, I would create an empty object "SpawnPoint", adjust its position and rotation and child it to the owner of the shooting script. Finally, would use a variable curBullet to show which bullet is currently selected:

var prefabs: GameObject[]; // assign the prefabs here in the Inspector
var curBullet: int = 0; // select the current bullet here

private var spawnPoint: Transform; // defines the position/direction
private var bulletSpeed: float = 20; // bullet speed

function Start(){
  // find the spawn point once at Start:
  spawnPoint = transform.Find("SpawnPoint");
}

// shoot the bullet selected by the indx parameter:

function Shoot(indx: int){
  var bullet: GameObject = Instantiate(prefabs[indx], spawnPoint.position, spawnPoint.rotation);
  bullet.rigidbody.velocity = spawnPoint.forward * bulletSpeed;
  Destroy(bullet, 5); // bullet self-destructs in 5 seconds
}

function Update(){
  if (Input.GetButtonDown("Fire1")){
    // shot the current bullet
    Shoot(curBullet);
  }
}

Change curBullet to select a different bullet.