If Take-Two Interactive's (Nasdaq: TTWO) Grand Theft Auto IV becomes a hit, don't be surprised to see Amazon.com (Nasdaq: AMZN) laughing all the way to the bank.

Yes, Amazon will profit from video game sales. After the game made its debut this morning, different versions of the title took up four of the seven best-seller slots in Amazon's online video game store. However, what's really noteworthy is that Amazon's fledgling MP3 downloading service is about to get a major boost by being worked into the game.

Music is a major part of GTA4. Players can choose from 16 in-game radio music stations that offer roughly 200 songs as they assume the role of Niko Bellic on the rough and tumble streets of Liberty City. A gamer can easily look up the artist and title of the song and tag it along the way. Players can look up the songs that they have tagged during the game when they log into Take-Two's new social-networking site and purchase high-quality MP3s of the songs through Amazon.com.

This is a sweet move for Amazon. The leading e-tailer recently overtook Wal-Mart (NYSE: WMT) to become the country's second-biggest seller of music files. It's still selling just a tenth of the tunes being dispensed by iTunes giant Apple (Nasdaq: AAPL), but that's also why the deal with Take-Two is so important.

Amazon knows it can't make its music store a winner simply by virtue of being Amazon. It needs a little help from its friends. That was obvious when it teamed up with PepsiCo (NYSE: PEP) a few months ago, to give away as many as a billion songs. That deal helped consumers associate Amazon with legal downloads. Now it's moving into the promotion of actual sales by integrating itself into what promises to be one of the hottest video games of the year.

Is it ironic that a company is promoting legal downloads in a game that's notorious for depicting illegal activities? Maybe, but why read too much into Amazon's perfect opportunity to eat into Apple's market share? Whether you're talking market share or cars, it's all about stealing when you're presented with opportunities.

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Amazon.com and Apple are Motley Fool Stock Advisor recommendations. Take-Two is a Rule Breakers newsletter service pick. Wal-Mart has been singled out in Inside Value. Try out any of these services free for 30 days.

Longtime Fool contributor Rick Munarriz has played a bit of Grand Theft Auto, but not enough to rush out for today's new installment. He does not own shares in any of the companies in this story. He is also part of the Rule Breakers newsletter research team, seeking out tomorrow's ultimate growth stocks a day early. The Fool has a disclosure policy.