MTV and Microsoft are set to take the wraps off their joint assault on Apple's iTunes, releasing a public beta of the long-awaited Urge on Wednesday.

Urge, first announced last December and touted by Bill Gates and Justin Timberlake at CES in January, will seek to challenge both the 99-cent "a la carte" downloads of iTunes and the monthly subscription services from Rhapsody, Napster, and Yahoo Music Unlimited.

Because of the ubiquity of the Windows Media Player 11 into which it will be integrated, Urge could present the best challenge yet to iTunes, but it still faces the same problem that has plagued all of the pretenders: lack of interoperability with the iPod.

That's right, despite packing the powerful MTV brand and the technology heft of Microsoft into one punch, music downloaded on Urge won't play on the world's most dominant portable music player.

But even though iPod's share of the digital music player market has grown from 26 percent in 2003 to nearly 80 percent for the first quarter of this year, Urge hopes to circumvent the iPod.

"We will concentrate on people who don't have iPods," Van Toffler, president of MTV Networks, told the Financial Times.

To do that, Microsoft brought in some of the companies that have been battling it out for the market share that Apple hasn't swallowed, including Samsung, Creative, and iRiver.

iRiver sent a team of engineers to Microsoft's Redmond, Washington, headquarters as it designed its latest device, the iRiver Clix, which is an update of its iRiver U10 model. The 2GB player was built specifically to work with Urge and Windows Media Player 11 in the hopes of mirroring the user experience of how well the iTunes store and the iPod players work together.

iRiver CEO Jonathan Sasse told MP3.com last month that more integration between stores like Urge and players like the iRiver Clix will put a dent in Apple's lead.

"We are going to see an environment in the next couple of months where it will be very easy to sit down and compare the offerings side by side," Sasse said at the time. "And what you'll see is something that will be as good or better than [iPod and iTunes]. That will start to resonate."

Urge will be available as an upgrade later this week or as a download from the Urge or Windows Media Player Web sites on Wednesday.

The service will launch with more than 2 million songs from 110,000 artists, 500 playlists, 130 streaming radio stations, and 24 genre-specific music blogs.

Users will be able to buy and own individual songs for 99 cents apiece or most albums for $9.99. Urge will also sell subscriptions, charging users to rent unlimited access to its music catalog as long as they continue to pay the monthly fee. Urge will charge $9.95 a month or $14.95 if subscribers want to load the music onto a portable player--prices that are in line with the other major subscription services.

Urge will surely rely heavily on the MTV brand and its long history as a place where young people go to find out about new music. MTV has said that Urge will include loads of MTV-exclusive content, including artist performances on such hit MTV shows as TRL and MTV Unplugged.

With iTunes having sold its one billionth download last month and continuing to grow its video catalog, Urge could face an uphill battle in the short term.

But MTV Networks chief digital officer Jason Hirschhorn told Macworld that the fight for the top slot in the digital music game is far from over.

"Clearly iTunes is leading the pack," he said. "It's not about trying to get people away from iTunes; for us it's about talking to the 95 percent of people that aren't buying online music yet."