> I am trying to create a html version of a dynamic website 
> so I can get better listing on search engines. Is there a 
> way way to download only the changes after the initial 
> download?
It only depends on the server abilities to handle update 
requests (using Last-Modified date, and/or Etag)

> Also, from the html version I would like the user to go 
> the actual website when he logins in or when adding 
> products to the shopping cart. Do I have to alter any 
> options for me to so this?
For shopping card: httrack never crawls forms (POST data), 
so it should be okay. To be sure, exclude in an explicit 
way shopping/login areas using 'Set Options'/'Scan rules', 
using something like:

-www.example.com/login/*
-www.example.com/shopping.php*