Wal-Mart is boxing out Redbox. Wal-Mart WMT, the world's largest retailer, has imposed strict limits on the number of DVDs any one customer can buy at a time, making it harder for movie-rental kiosks such as Coinstar's CSTR Redbox to get their hands on large numbers of newly released discs.The new rules took effect Feb. 1 and include a five-DVD cap on new releases, mirroring limits placed by Target TGT in December. Target's cap remains in effect for one week to several weeks after a movie is released to stores.