Grid thumbnails XML - rollover mod?

programming flash
1

I used the code from this thread to build a slideshow with two rows of thumbs. However I’d like to change the rollover style. Right now these two pieces of code:
[AS]
this.createEmptyMovieClip(“kk”,1029);
kk._x = 20;
kk._y = kk.starty=350;
kk.setMask(mm);
btn.enabled = false;
function drawSquare(clip, depth, colour, x, y, w, h) {
var mc = clip.createEmptyMovieClip(“clip”+depth, depth);
mc._x = x;
mc._y = y;
mc.lineStyle(2);
mc.beginFill();
mc.lineTo(w,0);
mc.lineTo(w,h);
mc.lineTo(0,h);
mc.lineTo(0,0);
mc.endFill();
return mc;
}
[/AS]
and later
[AS]
function sload() {
for (var i = 0; i<image.length; i++) {

	var clip = drawSquare(kk, i, 0, 0, 0, 60, 48);

	clip._x = (i%columns)*spacex;
	clip._y = Math.floor(i/columns)*spacey;
	if (i%6 == 0) {
		oarray.push(clip._y);
	}
	var clap = clip.createEmptyMovieClip("tt", 1);
	clap._x = 0;
	clap._y = 0;
	cliparray.push(clap);
	clip.imageHolder_mcValue = i;
	clip.onRelease = function() {
		p = this.imageHolder_mcValue-1;
		nextImage();
	};
	clip.onRollOver = function() {
		this._alpha = 50;
	};
	clip.onRollOut = function() {
		this._alpha = 100;
	};
}
startload();

}
[/AS]
create black background (I added an outline) behind each thumb. Then when mouse rolls over a tumb it’s opacity drops to 50% revealing the background.
What I would like to do is to move the black squares on top of the thumbs and affect THEIR opacity with the rollover action. Once I know how to do that I could move on and play with outline colors.

So I guess the first thing would be to choose the correct depth for both the thumbs and their background and then assign the rollover action to the - then - foreground squares. I can’t figure it out.
The full code is included in the thread mentioned on top.