Script to bring up GUI when player hits tagged object?

Pretty simple script but I have no idea!

var showGUI: boolean; 

function OnCollisionEnter(coll: Collision) { 
    showGUI = true; 
} 

function OnCollisionExit(coll: Collision) { 
    showGUI = false; 
} 

function OnGUI() { 
    if (showGUI) { 
            GUI.Box (Rect (10,10,100,90), "Loader Menu");

    // Make the first button. If it is pressed, Application.Loadlevel (1) will be executed
    if (GUI.Button (Rect (20,40,80,20), "Level 1")) {
        Application.LoadLevel (1);
    }

    // Make the second button.
    if (GUI.Button (Rect (20,70,80,20), "Level 2")) {
        Application.LoadLevel (2); 
    } 
}
}

And i only used this gui as a test

change

function OnCollisionEnter(coll: Collision) { 
    showGUI = true; 
} 

function OnCollisionExit(coll: Collision) { 
    showGUI = false; 
}

to

function OnCollisionEnter(coll: Collision) { 
   if(coll.gameObject.tag == "whatever tag")
   {
    showGUI = true; 
   }
} 
function OnCollisionExit(coll: Collision) { 
   if(coll.gameObject.tag == "whatever tag")
  {
    showGUI = false; 
  }
}