change texture problem

Hi, i have texture script which will make actual mouse cursor invisible and replaces the texture on it(mouse cursor will disappear and circle will appear in place of cursor)…
but the problem is if i attach the script to my Scene gameobject(which is empty) it will work exactly, but i have “Start” and “End” buttons and i want the texture to appear only when i click on “Start” Button… is there any statements which will add texture after pressing “Start” Button…
my script is here:

var myCursor:Texture2D;

var cursorSizeX: int = 50;

var cursorSizeY: int = 50;

function Start()

{

Screen.showCursor = false;

}

function OnGUI()

{

GUI.DrawTexture (Rect(Input.mousePosition.x-cursorSizeX/2 + cursorSizeX/2, (Screen.height-Input.mousePosition.y)-cursorSizeY/2 + cursorSizeY/2, cursorSizeX, cursorSizeY),myCursor);

}

I wrote this here, so no promises that it works. Should be self explanatory

var myCursor:Texture2D;
var cursorSizeX: int = 50;
var cursorSizeY: int = 50;

function Start()
{

}

function OnGUI()
{
    if(GUI.Button(Rect(0,0,10,10), "Start"))
    {
        ChangeCursor();
    }
    if(!Screen.showCursor)
    {
       GUI.DrawTexture (Rect(Input.mousePosition.x-cursorSizeX/2 + cursorSizeX/2, (Screen.height-Input.mousePosition.y)-cursorSizeY/2 + cursorSizeY/2, cursorSizeX, cursorSizeY),myCursor);
    }
}

function ChangeCursor()
{
    Screen.showCursor = false;
}