Where to start with ecommerce?

Hi, I am an amateur programmer looking to build an ecommerce site, but am a relative newcomer to the tools available (e.g. PHP and MySQL). I was just wondering if any of you have any recommendations as to where I should start gaining the knowledge necessary (e.g. books and tutorials). I am hoping to use open source code downloaded from oscommerce.com but need to understand it first!

Then, obviously, learning PHP is where to start. If you can't understand the code, you should start by looking up unfamiliar functions at www.php.net or a similar website.