Code:
<?php if (!defined ('ABSPATH')) die ('No direct access allowed'); ?><?php if (!empty ($gallery)) : ?>
<?php } ?>
<!-- Thumbnails -->
<?php foreach ( $images as $image ) : ?>
<?php if ( $image->hidden ) continue; ?>
<?php if ( $gallery->columns > 0 && ++$i % $gallery->columns == 0 ) { ?>
<?php } ?>
<?php endforeach; ?>
That should get you started. If you want it to work as a gallery on a template page.
BUT. The site you pointed to is not using the gallery function at all. Each one of those pics are a separate post. Looks like NextGen Gallery is just their means of upping and managing the pics (watermarks, cropping etc).
If you want something like the site you posted you just need to call out the featured thumbnail in the loop. Or you could use some fancy PHP which will pull the picture from the post automatically and make a thumb out of it.
That's as detailed as I'm going to get. It's not a lot of work.