X-cart USES Smarty. That's what the templates are comprised of, Smarty templates. So basically you have a huge smarty example infront of you with everything in skin1 folder and subfolders.
I found it pretty confusing at first, but once you dive into it, things become clearer.
I've found this site invaluable:
http://smarty.php.net/docs.php
HTH!
Carrie