Santa Monica-based Zag, the online car shopping web site headed by former CarsDirect founder Scott Painter, has inked a deal to power a new auto buying program with Overstock.com. Overstock.com said that Zag will connect customers with certified dealres on the firm's web site. Financial details of the deal were not disclosed. Zag has developed a web-based service which allows consumers to research, configure and price automobiles; the firm also has a number of deals with affiliate marketing organizations. Zag is venture backed by Anthem Ventures, Arcturus Capital, Capital One, Capricorn Management, GRP, and the Tech Coast Angeles.