Summer blockbusters have now begun to appear at DVD retailers and "rentailers" and are likely to boost business at those stores significantly in the months ahead, if the debut of the first one -- X-Men Origins Wolverine is any indication. The film, which earned $180 million at the box office, debuted in first place in sales and rentals last week, according to Nielsen VideoScan First Alert, which monitors sales, and Home Media Magazine , which monitors rentals. The movie reportedly sold more than 3 million copies during its first week in stores. By contrast, the No. 2 seller, the direct-to-video Barbie and the Three Musketeers, sold about 360,000 copies. ( Home Media pointed out, however, that Nielsen does not track sales at Wal-Mart, the nation's leading DVD seller and a big player in family and children's videos.)