The ecommerce toolkit is separate from eCart. You will be able to have more control over the cart if you use eCart instead of the eCommerce toolkit. You can use the User Registration Solution Pack with eCart pages to apply login capability to them.
Your friends over here at WebAssist! These Dreamweaver extensions will assist you in building unlimited, custom websites.
These out-of-the-box solutions provide you proven, tested applications that can be up and running now. Build a store, a gallery, or a web-based email solution.