function showAll(selector) {
    nodes = $$(selector);
    nodes.each(function(node) {
        node.show();
    });
}
function hideAll(selector) {
    nodes = $$(selector);
    nodes.each(function(node) {
        node.hide();
    });
}

function showImage(imageId) {
    hideAll('.image_container');
    $('image_container_' + imageId).show();

    nodes = $$('a.active');
    nodes.each(function(node) {
        node.removeClassName('active');
    });

    $('image_link_' + imageId).addClassName('active');
}