Collision problem

hi i'm going through a tutorial (http://www.youtube.com/watch?v=75AaGJIeaog) but i'm having problems even though i've followed the tutorial correctly.

heres the code

 #pragma strict
 
 var health : int = 100;
 var speed : int = 5;
 var collided_with = GameObject;
 
 function Start () {
 }
 
 function Update () {
     if(Input.GetAxis("Horizontal") > 0){
         if (collided_with != null){
             if (collided_with.tag == "Left"){
                 return;
             }
         }
         transform.Translate(Vector3(1 * speed * Time.deltaTime, 0, 0));
     }
     
     if(Input.GetAxis("Horizontal") < 0){
         if (collided_with != null){
             if (collided_with.tag == "Right"){
                 return;
             }
         }
         transform.Translate(Vector3(-1 * speed * Time.deltaTime, 0, 0));
     }
 }
 
 function OnCollisionEnter(col : Collision){
     collided_with = col.gameObject;
 }
 function OnCollisionExit(col : Collision){
     collided_with = null;
 }

i have 3 errors they are :

Assets/Scripts/player_Script.js(13,43): BCE0019: 'tag' is not a member of 'System.Type'.

Assets/Scripts/player_Script.js(22,43): BCE0019: 'tag' is not a member of 'System.Type'.

Assets/Scripts/player_Script.js(31,29): BCE0022: Cannot convert 'UnityEngine.GameObject' to 'System.Type'.

any help is appreciated