Billboard magazine is charting new territory this week, adding data for the first time on sales of Internet music downloads to its lists of top-selling albums.

Nielsen SoundScan, which tracks retail music sales and is the source of Billboard's top music charts, will make data available Wednesday on music downloads sold at several digital-tunes services. These include Apple Computer's iTunes, Roxio's Pressplay, MusicNet, Liquid Audio and Listen.com. It also plans to track sales from the upcoming Napster service.

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