Apple's Front-Runner Challenge

Apple (AAPL Quote) has raced to the front of the digital music market with its iPod line. But some are wondering how long it can stay in the pole position.

"We're still at the very early stages of this transition" to digital music delivery, said Mike McGuire, who covers the online music market as a research director at GartnerG2. "The game ain't over by a long shot."

How the competition ultimately turns out should have big implications for Apple's stock over the long term. Its shares tripled last year as booming iPod sales -- now more than one-third of the company's revenue -- revved up the company's earnings -- and its potential prospects. The stock's run has left it trading at a sharp premium to rivals such as computer industry leader Dell (DELL Quote). ...