variable for x, y position?

Hi, I have bought some code to make a starry night in my animation but I need to make this either only appear inside a movie clip, or on a certain part of the stage, can anyone tell me how to alter the below code so I can do this? do you I need to add in some x, y coordinates?

Thanks!

import mx.transitions.Tween;
import mx.transitions.easing.*;

var maxStars:Number = 25;
var minSize:Number = 50;
var maxSize:Number = 115;
var maxDuration:Number = 3;
var minDuration:Number = 1;
var windowWidth:Number = 100;
var windowHeight:Number = 100;

var stars:Array = new Array(maxStars);
var starsClip:Array = new Array(maxStars);
var starsTweenX:Array = new Array(maxStars);
var starsTweenY:Array = new Array(maxStars);

for (var init:Number = 0; init < maxStars; init++) {
/* Sets the duration for the star to appear */
var duration = Math.random() * (maxDuration - minDuration) + minDuration;

/* Attaches the Star movieclp to the Stage and sets its parameters */
_root.attachMovie("Star", "myStar"+init, _root.getNextHighestDepth());
_root["myStar"+init]._x = Math.random() * windowWidth;
_root["myStar"+init]._y = Math.random() * windowHeight;
_root["myStar"+init]._xscale = _root["myStar"+init]._yscale = Math.random() * (maxSize - minSize) + minSize;

/* Sets the twinkling of the stars */
starsTweenX[init] = new Tween(_root["myStar"+init], "_xscale", None.easeNone, _root["myStar"+init]._xscale, 0, duration, true);
starsTweenY[init] = new Tween(_root["myStar"+init], "_yscale", None.easeNone, _root["myStar"+init]._yscale, 0, duration, true);

/* Resets the stars once they've faded out */
starsTweenX[init].onMotionFinished = function() {
if (this.obj._xscale == 0) {
this.obj._x = Math.random() * windowWidth;
}
this.yoyo();
}
starsTweenY[init].onMotionFinished = function() {
if (this.obj._yscale == 0) {
this.obj._y = Math.random() * windowWidth;
}
this.yoyo();
}
}