switch scripts?

What you are doing is enabling/disabling the whole gameObject, not the script. For GameObjects, you should use SetActiveRecursively( true/false ), though this changed for Unity 4 (http://answers.unity3d.com/questions/359394/gameobject-setactiverecursively.html).

Typecast to the names of the scripts :

 var Script1 : NameOfScriptOnObject1;
 var Script2 : NameOfScriptOnObject2;

EDIT :

Create a new scene

Create an empty gameObject, call it HelloObject.

Create a script, call it HelloScript, paste this code :

 #pragma strict
 
 function OnGUI() 
 {
     GUI.color = Color.green;
     GUI.Box( Rect( (Screen.width*0.5) - 120, 40, 100, 35 ), "Hello ...." );
 }

attach HelloScript to HelloObject

Create an empty gameObject, call it GoodbyeObject.

Create a script, call it GoodbyeScript, paste this code :

 #pragma strict
 
 function OnGUI() 
 {
     GUI.color = Color.white;
     GUI.Box( Rect( (Screen.width*0.5), 80, 100, 35 ), ".... Goodbye" );
 }

attach GoodbyeScript to GoodbyeObject

Create an empty gameObject, call it SwapObject.

Create a script, call it SwapScript, paste this code :

 #pragma strict
 
 var theHelloScript : HelloScript;
 var theGoodbyeScript : GoodbyeScript;
 
 function Start() 
 {
     theHelloScript.enabled = false;
     theGoodbyeScript.enabled = false;
 }
 
 function Update() 
 {
     if (Input.GetMouseButtonDown(0))
     {
         theHelloScript.enabled = true;
         theGoodbyeScript.enabled = false;
     }
     else if (Input.GetMouseButtonDown(1))
     {
         theHelloScript.enabled = false;
         theGoodbyeScript.enabled = true;
     }
 }

attach SwapScript to SwapObject

Now, click on SwapObject, and look in the Inspector. There are 2 variables :

 var theHelloScript : HelloScript;
 var theGoodbyeScript : GoodbyeScript;

Now, try and drag HelloObject onto theGoodbyeScript first, see how it won't drop in. Now put it where you think it should really go. Now drag in GoodbyeObject.

Now hit, play, then click the left-mouse-button, then the right-mouse-button.