well firstly, open source does not mean you can see the source, it means you have a right to use the source to develop new code.
secondly, there is no possibility of windows' source code ever being released to the public as it would compromise a great deal of software in microsoft's current products which is unstable and insecure. they have stated this publicly, and even in court as part of a defense argument i believe! unlike most other popular operating systems microsoft windows really is too far down the road to ever be fixed up, in terms of security and stability, to the point where it can safely have the source code available to be viewed by just anyone.
to me, this makes it a failure as a secure and viable operating system.