the image probably wont point to the productID unless the product id is also the file name for the image.
in many cases, there would be an image column in the cart that would hold the file name.
The tutorial follows the eCommerce database:
in the product table for this database, there is a ProductLocation column that is used in the download behavior to get the file name for downloading.
you are going to need to set the cart up to show the download link if the chose the download option.
You wont be able to uplaod the files outside of the sites root using Dreamweaver, you will need to use a separate standalone ftp program like file zilla.