On WebReference.com today there's a quick guide to helping you get an e-commerce site set up easily for your WordPress installation. It uses the WP e-Commerce plugin to make it all work.

The readymade e-commerce tool that Jason used is actually a plug-in for WordPress called WP e-Commerce. The basic version is free, and you can buy additional modules. In the following sections, I will explain how you can install and set up your e-commerce site using WP e-Commerce.

They show you how to install the plugin, set up a theme (a WordPress layout that makes the most of the plugin) and how to set up things like the products, variations on them and configure some of the settings that come with it.