The duo of Alex Rigopulos and Eran Egozy may one day leave their indelible imprint on pop-music history. When it comes to music games, however, the founders of the Cambridge, Mass.-based Harmonix have already secured their place in the pantheon. Their work on Guitar Hero I and II, which invigorated the music-videogame category in the United States, would have been enough. But in November, the company again reinvented the genre with Rock Band, pairing a faux drum kit and a karaoke microphone with a mock guitar for the ultimate ersatz group. "Our original mission statement was to bring the joy of music making to everyone out there in the world who may not necessarily have all the experience that comes from having learned a real musical instrument," says Egozy, a talented clarinetist. "We had no idea that it would become this huge."