Event.observe(document, 'dom:loaded', function() {
    prodImageRollOver();
});

//shows rollover image
//this works by adding a class .switch to the dom elements affected
//needs css to work properly
function prodImageRollOver() {

    var links = $$('.grid-row .product-image');    
    links.each(function(item) {
        Event.observe(item, 'mouseover', function() {

            item.addClassName('switch');
        });
        Event.observe(item, 'mouseout', function() {
            item.removeClassName('switch');
        });
    });
}