It's an e-business enigma. PC owners are looking for more and more of their entertainment online, as Napster and its subscription-based successors have shown. And many of the companies that own today's most popular songs, books and movies are eager to sell their content over the Internet-if only they can find a way that's both convenient for customers and profitable for copyright owners. Yet many of the "digital rights management" companies that were founded to provide just such an online marketplace are shrinking or even disappearing from sight.

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