Wal-Mart plans to launch its own online music downloading service. The retailer is looking to its core customer base with its new online music service, offering a library of largely country songs for less than the standard 99 cents per song. The retailer sells 20 percent of the nation`s recorded music. Bentonville-based Wal-Mart already rents DVDs online, and analysts say offering music opens the market to a new demographic. Wal-Mart`s service may be online as soon as next week and carry about 200,000 -- half the library of some other downloading sites. During the summer, Wal-Mart completed a seven-month trial and began full-scale operations in its online DVD rental business, a challenge to market leader Netflix.