Parsing error,

using UnityEngine;
using System.Collections;

#pragma strict

public var one : Camera ;
public var two : Camera ;


function Start() {
	one.Camera.enabled = true;
	two.Camera.enabled = false;
}

function Update() {
	if(Input.GetButtonDown("switch"))
	{
		one.Camera.enabled = !one.Camera.enabled;
		two.Camera.enabled = !two.Camera.enabled;
	}
}

Use import instead of using

Cameras don’t have a public static Camera property.

 import UnityEngine;
 import System.Collections;

 #pragma strict
 
 public var one : Camera ;
 public var two : Camera ;
 
 
 function Start() {
     one.enabled = true;
     two.enabled = false;
 }
 
 function Update() {
     if(Input.GetButtonDown("switch"))
     {
         one.enabled = !one.enabled;
         two.enabled = !two.enabled;
     }
 }