The Files for that tutorial are only available if you have purchased eCart 4. That Tutorial Is specific to eCart 4 and Site Assist.
Using eCart 5, and Data Bridge: the Data Bridge the "Integrating Data Bridge and eCart" tutorial is a good place to start for using Data Bridge to create the Catalog pages and then adding the eCart add to cart buttons:
http://www.webassist.com/community/tutorials/view_tutorial.php?tid=22