how to add texture?

in this code how do i give texture to get set,ready and go in this code

function Start ()
{
// Disable AI Cars
aiCars = FindObjectsOfType (SeekSteer);
for (var car : SeekSteer in aiCars)
car.enabled = false;

// Disable Player Cars
playerCars = FindObjectsOfType (Car);
for (var car : Car in playerCars)
	car.enabled = false;

// Display get ready, wait
guiText.text = "Get Ready";
yield WaitForSeconds (1.50);

// Display Set, wait
guiText.text = "Set";
yield WaitForSeconds (1.50);

// Display go and enable all cars
guiText.text = "Go";
aiCars = FindObjectsOfType (SeekSteer);	
for (var car : SeekSteer in aiCars)
	car.enabled = true;

// Enable Player Cars
playerCars = FindObjectsOfType (Car);
for (var car : Car in playerCars)
	car.enabled = true;

// Wait and Hide text
yield WaitForSeconds (1.50);
guiText.text = "";

}

please help!!
thanx!!

// variables

var countdown3 : Texture2D; // ready - put picture in inspector    
var countdown2 : Texture2D; // set    
var countdown1 : Texture2D; // go    

private var countdown : Texture2D;    
private var showCountdown : boolean = false;

// ----

// call this function to display countdown
function getReady ()    
{
	showCountdown = true;    

	countdown = countdown3;    
	yield WaitForSeconds (1.5);  

	countdown = countdown2;    
	yield WaitForSeconds (1.5);

	countdown = countdown1;    
	yield WaitForSeconds (1.5);
   
	showCountdown = false;
}

// ----

// GUI
function OnGUI ()
{
	if (showCountdown)
	{    
		// Get Ready countdown   

		// Make a group on the centre of the screen    
		GUI.BeginGroup (Rect (Screen.width / 2 - 100, 50, 200, 175));

		// Make a box to show the group on the screen	    
		GUI.color = Color.red;    
		GUI.Box (Rect (0, 0, 200, 175), "GET READY");

		// display countdown    
		GUI.color = Color.white;    
		GUI.Box (Rect (10, 25, 180, 140), countdown);

		// End GUI group class    
		GUI.EndGroup ();
	}    
}

// ----