They seriously got into it around 2007. They even had their own mall kiosks. It was part of the industry shift into cheap assembly in China. (Apple made the shift too, they ended US assembly around 2003.)
The end of Dell's shift happened around last year. With their margins so low, they can't afford to air freight computers or manage a dynamic supply chain anymore. Build-to-order options are gone for all but large corporate orders and high-margin gaming systems. Everything is basically sold from stock, fitting in well with the retail store model.
found this on wikipedia:
In the early 1990s, Dell sold its products through Best Buy, Costco and Sam's Club stores in the United States. Dell stopped this practice in 1994, citing low profit-margins on the business, exclusively distributing through a direct-sales model for the next decade. In 2003, Dell briefly sold products in Sears stores in the U.S. In 2007, Dell started shipping its products to major retailers in the U.S. once again, starting with Sam's Club and Wal-Mart. Staples, the largest office-supply retailer in the U.S., and Best Buy, the largest electronics retailer in the U.S., became Dell retail partners later that same year.