Help with arrays as image viewer

1

I have 10 pictures (using arrays) appearing ramdomly and I need to center them (what should i use? _x, _y…). Also, I have to create one back button and one next button. what script should I apply to these buttons? Please see my script below. thanks for your help.

this.onLoad = function(){
mypictures = [“tibet.jpg”, “tibet2.jpg”, “camel.jpg”, “forest.jpg”, “einstein.jpg”, “bear.jpg”, “dragon.jpg”, “af1.jpg”, “ceppu.jpg”]
numPics = mypictures.length;
randomNum = Math.random(numPics);
trace(randomNum);
randomNum = randomNum * numPics;
trace(randomNum);
randomNum = int(randomNum);
trace(randomNum);
thisTime = mypictures[randomNum];
trace(thisTime);
this.createEmptyMovieClip(“imageHolder_mc”, 1);
imageHolder_mc.loadMovie(thisTime);
imageHolder_mc._x = Stage.width/2;
imageHolder_mc._y = Stage.height/2;
this._x = 0;
this._y = 0;

this._xscale = 50;
this._yscale  = 50;
_root.photo_name.text = thisTime;

}

stop();