Bookseller Barnes & Noble on Monday announced that it will spin out its Nook business and that software giant Microsoft will invest $300 million in the new company, setting it up in competitionwith crosstown technology company Amazon.com. Microsoft will own 17.6% of the temporarily named "NewCo," valuing the Nook business at $1.7 billion. The partners said the investment would allow NewCo to accelerate the introduction of the Nook bookstore in international markets and to give a shot of innovation to the development of new e-ink Nook readers and tablets. The companies didn't say anything about new products, other than that NewCo will develop a Nook app forMicrosoft's new Windows 8 operating system. But it's reasonable to assume that future Nooks will now tilt toward Microsoft's platforms.