Modifications to include a lightbox effect with the post attachment automatic slide output: http://revelationconcept.com/wordpress-display-all-post-attachment-images-in-a-slider/

post-attachment-slider-lightbox

// Add this after line 18 in the example:

    $thumb_array = image_downsize( $image->ID, 'your-custom-image-size' );
    $thumb_url = $thumb_array[0];

// Now, you will need to modify the output to include your thumbnail image, a link to the full image and your lighbox classes. So lines 20-28 should look something like this:

    echo '<li>';
    echo '<a class="your-lightbox-class" href="';
    echo $img_url;
    echo '">';
    echo '<img src="';
    echo $thumb_url;
    echo '" alt="';
    echo $img_alt;
    echo '" title="';
    echo $img_title;
    echo '" />';
    echo '</a>';
    echo '</li><!--end slide-->';