My Apologies, I was incorrect in saying that it would work with CS3. The eBay store builder was discontinued before Dreamweaver CS3 was released.
eBay Store builder v 1.1.1 was the last update made. It was released on 11/4/2005 and is supported in Dreamweaver MX, MX2004 and Dreamweaver 8.
Dreamweaver CS3 was not released until 4/16/2007.