I'm not familiar with this system, are you able to edit individual pages in the site? So long as you can add server side code to the pages in your CMS and save pages to the same directory as these files reside then you should be able to integrate eCart. The first step in this is to open a page from the site in DW and create a new cart object. The overall process should not differ from any other type of site, I would suggest that you start with the getting started guide for eCart, here is a link:
We will not be able to offer you a specific set of steps for integrating the cart with your setup but if you run into any problems or have any questions about any specific part please let us know and we will do what we can to help you out with this.