How did they do this image gallery on the products?
 

How do they do the Have 1 product but show 20 different colors of the product in small images beside of it that you can click on

here is an example:
http://www.shirtshop.nl/xcart/customer/product.php?productid=1904&cat=0&page=

That is a custom mod for sure. Also, please put your X-Cart version in your signature, we can't help you without it. Edit profile, enter version, enter help desk password, click the 'Always attach my signature:' box, save. Thanks!

is that something they built or a add onthey bought?

ver 4.0.17
add: affiliates

There used to be a mod floating around that did this, but the company who sold it was blacklisted by X-Cart, so it is no longer available.

So there is no way to get one and intergrate it anymore?

ver 4.0.17
add: affiliates

Not if you want your X-Cart licence to remain valid :) I'd suggest posting in the Pro Services - Requests forum, or contacting X-Cart about creating the mod for you. There is this mod that does something similar to that:

http://forum.x-cart.com/viewtopic.php?t=19259