Thumbnail scroller

I need to edit this code


function thumbNailScroller() {
this.createEmptyMovieClip("tscroller", 1000);
scroll_speed = 10;
tscroller.onEnterFrame = function() {
if ((_root._xmouse>=thumbnail_mc._x) && (_root._xmouse<=thumbnail_mc._x+thumbnail_mc._width)) {
if ((_root._ymouse>=(hit_right._y-40)) && (thumbnail_mc.hitTest(hit_right))) {
thumbnail_mc._y -= scroll_speed;
} else if ((_root._ymouse<=(hit_left._y+40)) && (thumbnail_mc.hitTest(hit_left))) {
thumbnail_mc._y += scroll_speed;
}
} else {
delete tscroller.onEnterFrame;
}
};
}

So that the thumbnails scroll when a btn is pressed. I do not want scrolling based on mouse position. I have two columns of thumbnails and I want the thumbnails to scroll when an up and down arrow are pressed. I also need the buttons to be disabled when the thumbs reach the beginning and the end. Can anyone help me?