osCommerce is the leading Open Source online shop e-commerce solution that is available for free under the GNU General Public License. It features a rich set of out-of-the-box online shopping cart functionality that allows store owners to setup, run, and maintain their online stores with minimum effort and with no costs, license fees, or limitations involved.

• Installing osCommerce
• Configuring your store
• Adding categories
• Adding products
• Adding product attributes
• Configuring currency
• Adding payment modules
• Adding shipping modules
• Configuring sales tax
• Editing your home page
• Editing left and right columns
• Editing your header and footer
• Creating specials
• Managing customers
• Sending out a newsletter
• Sending out email
• Mangaging your banners
• Backing up and restoring your database

If you are intending to process payments online then you should consider securing your e-commerce site with an SSL certificate.

For payment processing in Ireland there are a number of options including Paypal, Realex Payments and 2Checkout to name but a few.