I use this one:

var originalCursor : Texture2D;


var cursorSizeX: int = 32;  // set to width of your cursor texture
var cursorSizeY: int = 32;  // set to height of your cursor texture

static var showOriginal : boolean = true;

function Start(){
Screen.showCursor = false;
//Screen.lockCursor = true;
}


function OnGUI(){

    if(showOriginal == true){
        GUI.DrawTexture (Rect(Input.mousePosition.x-cursorSizeX/2 + cursorSizeX/2, (Screen.height-Input.mousePosition.y)-cursorSizeY/2 + cursorSizeY/2, cursorSizeX, cursorSizeY),originalCursor);
    }


}

one question why do you minus screen height

Note these techniques have been rendered obsolete by http://docs.unity3d.com/Documentation/ScriptReference/Cursor.SetCursor.html

IT IS WORK IN CENTER OF CURSOR for you

var originalCursor : Texture2D;


var cursorSizeX: int = 128;  // set to width of your cursor texture
var cursorSizeY: int = 58;  // set to height of your cursor texture

static var showOriginal : boolean = true;

function Start(){
//Screen.showCursor = false;
//Screen.lockCursor = true;
}


function OnGUI(){

    if(showOriginal == true){
        GUI.DrawTexture (Rect(Input.mousePosition.x-cursorSizeX/2 + 1, (Screen.height-Input.mousePosition.y)-cursorSizeY/2 + 1, cursorSizeX, cursorSizeY),originalCursor);
    }


}

You could also use the framework: http://edrivenunity.com/cursors