Navmesh Trouble

Hi all. I'm starting to learn Unity's navmesh system, and I've been trying to apply it to an AI script I have already scripted. (Below) How can I make it so that it uses the navmesh agent in this script? Thanks!

 var agent : NavMeshAgent = GetComponent.<NavMeshAgent>();
  
 //wandering vars
 public var wanderSpeed = 2.0;
 public var wanderRotSpeed = 5.0;
 public var wanderRadius = 10.0;
 public var wanderRayDistance = 5.0;
 public var wanderPauseMin = 2.0;
 public var wanderPauseMax = 6.0;
 private var basePosition : Vector3;
 private var currentDestination : Vector3;
 var walk : AnimationClip;
  
 //chase vars
 var chaseDistance : float = 10.0;
 var chaseSpeed : float = 3.0;
 var chaseRotSpeed : float = 5.0;
 var run : AnimationClip;
  
 //attack vars
 var attackDistance : float = 3.0;
 var attackRate : float = 0.25;
 var attack : AnimationClip;
  
 //state setup
 var state : aiState;
  
 InvokeRepeating("StateLogic", 0.0, 0.05);
  
 function Start(){
     if(target == null)
         target = GameObject.FindWithTag("Player").transform;
     ChooseNextDestination();
     yield StateMachine();
 }
  
 function StateLogic(){
     var distanceToTarget = (target.position - transform.position).sqrMagnitude;
     if(distanceToTarget <= attackDistance*attackDistance)
         state = aiState.attacking;
     else if(distanceToTarget <= chaseDistance*chaseDistance)
         state = aiState.chasing;
     else
         state = aiState.wandering;
 }
  
 function StateMachine(){
     while(true){
         switch(state){
             case aiState.wandering:
                 yield Wander();
                 break;
             case aiState.chasing:
                 Chase();
                 break;
             case aiState.attacking:
                 yield Attack();
                 break; 
         }
         yield;
     }
 }
  
 function Wander(){
     RotateToward(currentDestination, wanderRotSpeed);
     MoveForward(wanderSpeed);
     //BroadcastMessage("PlayAnimation", "walk");
     var destPosZeroY = currentDestination;
     var currentPosZeroY = transform.position;
     destPosZeroY.y = 0;
     currentPosZeroY.y = 0;
     if((destPosZeroY - currentPosZeroY).magnitude < 1.0){
         yield WaitForSeconds(Random.Range(wanderPauseMin, wanderPauseMax));
         ChooseNextDestination();
         animation.Play("walk");
     }
 }
  
 function ChooseNextDestination(){
     var randOffset : Vector2 = Random.insideUnitCircle * wanderRadius;
     currentDestination = basePosition + new Vector3(randOffset.x, transform.position.y, randOffset.y);
     Debug.DrawLine(transform.position, currentDestination, Color.white);
 }
  
 function Chase(){
     RotateToward(target.position, chaseRotSpeed);
     MoveForward(chaseSpeed);
     animation.Play("run");
  }
  
 function Attack(){
     yield WaitForSeconds(attackRate);
     animation.Play("attack");
 }
  
 function RotateToward(targetPos : Vector3, rotSpeed : float){
     targetPos.y = transform.position.y;
     var rotation = Quaternion.LookRotation(targetPos - transform.position);
     transform.rotation = Quaternion.Slerp(transform.rotation, rotation, Time.deltaTime * rotSpeed);     
 }
  
 function MoveForward(moveSpeed : float){
     transform.Translate(Vector3.forward*Time.deltaTime*moveSpeed);
 }