According to insiders and Microsoft partners, a "Milestone 1 code drop" has been released of the next-gen Windows OS. This, along with an updated roadmap leaked to TGDaily, points to a release window of 2nd Half 2009. Among the new features seen in the really, really early M1 release are combining multiple graphics cards from different vendors into one graphics system, and a new version of Media Center.

It's still unclear when the first beta versions will be available (meaning when the developer community at large will be able to test it), but guesses point to early 2009.

Source- http://gizmodo.com/346711/windows-7-to-be-released-ahead-of-schedule