E-commerce website

Someone has asked me to design them a webstore for their antiques business, currently run as an ebay store.

I'm a professional graphic designer who has dabbled with web design over the years. I can code HTML, know my way round CSS, Flash, PHP/MySQL. However I've never created an e-commerce site.

Can someone recommend my best route? Do I use an online e-commerce service? Should I design the site and get a professional web design company to create the e-commerce part? Or is it not as hard as I imagine to create a store from scratch?

Thanks folks.