You could create this site using the Super Suite extensions, or you could use Power Store.
We did a webinar a little while back on Power Store, this webinar includes detailed instructions for edit the power store theme or using your own theme:
http://www.webassist.com/product/powerstore-webinar
if you decide to go the route of using the super suite extensions for creating your store, see the eCommerce tutorials series:
http://www.webassist.com/tutorials/eCommerce-Overview-eCommerce-Series