On the Developer Tutorials site today, there's a new look at working with the Drupal e-Commerce module in your Drupal installation.

What if you [also] want to support collaborative editing of content, community forums, and other capabilities that could help increase traffic to your site, but are usually only found in content management systems (CMSs)? Is it possible to combine the best of both worlds - shopping carts and CMSs? Fortunately, the answer is yes, if you choose a world-class CMS such as Drupal as a foundation for your site.

They walk you through how to get the module installed, how to configure it to match with your site's layout and flow and how to hook the purchase process into PayPal to make purchasing a few simple user clicks away.