Optimizing photo galley

1

I have this code like a every other gallery with thumbs and everytime you click on one of the thumbs the image selected appears

var thumb_spacing = 49;

// load variables object to handle loading of text
var description_lv = new LoadVars();
description_lv.onData = function(raw_text){
    description_txt.text = raw_text;
}

function GeneratePortfolio(portfolio_xml){
    var portfolioPictures = portfolio_xml.firstChild.childNodes;
    for (var i = 0; i < portfolioPictures.length; i++){
        var currentPicture = portfolioPictures*;
        
        var currentThumb_mc = sub_display.createEmptyMovieClip("thumbnail_mc"+i,i);
        currentThumb_mc._x = i * thumb_spacing;
        
        currentThumb_mc.createEmptyMovieClip("thumb_container",0);
        currentThumb_mc.thumb_container.loadMovie(currentPicture.attributes.thumb);
        
        currentThumb_mc.title = currentPicture.attributes.title;
        currentThumb_mc.num = currentPicture.attributes.num;
        currentThumb_mc.image = currentPicture.attributes.image;
        currentThumb_mc.description = currentPicture.attributes.description;
        
        
        currentThumb_mc.onRollOver = currentThumb_mc.onDragOver = function(){
            title_txt.text = this.title;
            num_txt.text = this.num;
            
                    }
        currentThumb_mc.onRollOut = currentThumb_mc.onDragOut = function(){
            title_txt.text = this.title;
            num_txt.text = this.num;
        }
        currentThumb_mc.onRelease = function(){
            place_holder.loadMovie(this.image);
            
            description_lv.load(this.description);
        }
    }
}

// xml object for xml content (defines sources for selections)
var portfolio_xml = new XML();
portfolio_xml.ignoreWhite = true;
portfolio_xml.onLoad = function(success){
    if (success) GeneratePortfolio(this);
    else trace("Error loading XML file"); // no success?  trace error (wont be seen on web)
}
// load
portfolio_xml.load("portfolio.xml");

But i want so that everytime you rollover or hover on one of the thumbs it expands

I cant get it to work

Help appreciated