function showCompagnyImage()
{
    $('mainimage').getElementsByTagName('img')[0].src = url_to_root + 'images/' + this.getElementsByTagName('a')[0].getAttribute('rel') + '.jpg';
    $('mainimage').getElementsByTagName('a')[0].href  = this.getElementsByTagName('a')[0].href;
}

Event.observe(window,'load',function() {
    $$('#home_rechts .bedrijf').each(function(item){
        item.observe('mouseover',showCompagnyImage);
    });
});