As a quick and less painful way of starting trading you can always use all in one providers, we started our first online store using Demon Commerce, this provides the store database, checkout functionality and sets up a merchant account for credit card processing.
It does restrict you to all the above and as time goes on you may want to escape as turnover increases and functionality becomes limiting, but as a start it is not a bad package.
http://www.demon.net/products/demoncommerce/
http://www.demon.net/helpdesk/produc...e/d-faq1.shtml