moving and rotating my object in 3d

I'm making a flight game and I'm currently just trying to get my ship to move at a constant speed and be able to turn in 3 dimensions. If i don't use my moveforward.js file, everything works fine, the camera follows behind the ship as it rotates and its great. but there seems to be a compounding problem when i add velocity along the objects z axis. if i turn more than 90 degrees in any direction the ship still wants to go in a positive z direction( relative to the world). so i start flying backwards. Here are my files:

movedirection.js (attached to the ship)

var turnspeed : float= 6.0;

function Update () {

var x = Input.GetAxis("Horizontal") Time.deltaTime turnspeed; var z = Input.GetAxis("Vertical") Time.deltaTime turnspeed; transform.Rotate(z, 0, -x);

}

moveforward.js (attached to the ship)

var speed : float=1.0; function FixedUpdate () {

moveDirection = transform.TransformDirection(Vector3.forward)*Time.deltaTime*speed;

transform.Translate(moveDirection);

}

follow.js (attached to the chase camera)

var target : Transform;

var distance = 1.6;

var damping =2.0;

var smoothRotation = true;

var rotationDamping =2.0;

function LateUpdate() {

 var wantedPosition = target.TransformPoint(0, 0, -distance);

     transform.position = Vector3.Lerp (transform.position, wantedPosition,

     Time.deltaTime * damping);

if (smoothRotation) {

     var wantedRotation = Quaternion.LookRotation(target.position -   

     transform.position, target.up);

     transform.rotation = Quaternion.Slerp (transform.rotation, wantedRotation,  

     Time.deltaTime * rotationDamping);

}

else transform.LookAt (target, target.up);

}.

I think I'm just to close to the problem right now, its like its on the tip of my tongue and I can't quite get it.