The beta, or test, version of the service launched in the United States, dubbed "URGE," offers downloads from a catalog of two million songs for 99 cents, the same price as iTunes.
It also will feature 130 CD-quality radio stations in a variety of musical genres and 500 "playlists" for subscribers of a service paying about 10 dollars a month or 99 dollars a year. URGE is offering a 14-day free trial for the service.
International versions of the store will depend on the success of the US version, which will have an updated service later this year.
The move came as Microsoft announced the availability of a new version of its Windows Media Player software, which was said to be "seamlessly" integrated in the URGE service.
Mike Sievert, corporate vice president of Windows Client Marketing at Microsoft, said the new Media Player 11 "incorporated a significant amount of feedback from music fans and worked hand in hand with MTV Networks."
"As a result, Windows Media Player 11 truly revolutionizes the way we enjoy music and provides a test drive of the breakthrough entertainment capabilities people will experience in the forthcoming Windows Vista operating system," he said.
"When we first set out to design URGE, our goal was to create an immersive experience that surrounded fans in all things music," said Van Toffler, president of MTV Networks Music.
"URGE distinguishes itself through handcrafted programming, innovative music discovery features and unique integration with Windows Media Player 11. It's an important pillar of MTV Networks's overall digital strategy, and as our audience continues to embrace digital music delivery, URGE will serve as a vital vehicle to connect fans with all the music they love."
It remains unclear whether URGE can make a dent in the domination of Apple and iTunes, which has sold over one billion songs worldwide and holds as much as 80 percent of the global marketplace.
Analysts say one reason for Apple's success is the integration of the iTunes store with its wildly popular iPod music player.
"At this point, I don't see URGE as any serious threat to iTunes or iPod," said Joe Wilcox at Jupiter Research.
"Major reason: It's beta. Microsoft, MTV and hardware partners are still assembling pieces and will continue to do so over the summer. The real test against Apple will start much later this year, when, presumably, music store, media player and hardware will be on the newest Windows Media technologies."
Still, the new service will carry clout from Microsoft and MTV, a unit of media giant Viacom, which has a global presence.
The launch may change the landscape in the so-called format war involving Microsoft and Apple. At present, songs downloaded in the Windows Media Audio (WMA) format cannot be played on iPods, and songs from iTunes cannot be played on WMA devices.