Jupiter Research today announced that it forecasts U.S. shipments of MP3 players will almost double in 2003 to over 3.5 million, and will continue to grow almost 50% per year for the next three years. “By 2006, the installed base of MP3 players will top 26 million, establishing a critical mass of users that will help spur digital music sales,” notes the firm. In addition Jupiter says that the “combination of Apple’s iPod device and its iTunes Store for music downloads has energized the music industry.