The units will be available starting February 1st, but you can pre-order yours right now for $249.99 on Amazon compared to the $100 - $150 retail pricing of it's Xbox counterpart.
The price different between the XBox version is justified with the improved features in the new Kinect. It features 'near mode' who lets you use it up close, a new firmware which allows the kinect to detect objects as close as 50cm away without loosing accuracy or precision.
It will be interesting to see how the new Kinect fits into Microsoft's Windows 8 release and the future of computing. The rather large Kinect wont be replacing your webcams, but it's potential lies with commercial developers who can build specialized applications for medicine or education using voice and gesture based interactions.
Microsoft further plans to make the Kinect for Windows available at just $150 for students, educators, schools, libraries and museums sometime in the near future.