Someone

onClipEvent (load) {
	for (i = 0; i < _root.totalFotos; i++) {
		this.createEmptyMovieClip(["th" + i], i);
		this["th" + i].loadMovie("th" + i + ".jpg");
		var pp = createEmptyMovieClip("preload" + i, i + 100);
		pp.id = i;
		pp.onEnterFrame = function() {
			if (this._parent["th" + this.id]._width > 0) {
				delete this.onEnterFrame;
				this.removeMovieClip();
			}
		}
		if (i == 0) {
			this["th" + i]._x = 0;
		} else {
			anterior = i - 1;
                        trace(anterior); // to see if it gets what you want.
			this["th" + i]._x = this["th" + anterior]._x + this["th" + anterior]._width;
		}
	}
}