The Windows 8 beta is likely to be released by late February 2012, according to news reports. The actual date of completion and shipment of Windows 8 operating system from Microsoft has not been revealed so far.
February is a bit late than what was expected, the operating system itself has been making steady progress. What will be there in the beta is also not known yet, because that may depend on the components that are ready at that time.
The Windows 8 Developer preview was released by Microsoft only few weeks back at the Build Developers Conference where it was very well received.
So it can now be expected that the Windows 8 based tablet would arrive after February next year.