Here is a statement from Microsoft regarding the current 
preliminary release of Windows NT and the subsequent beta
program this fall. I hope this will help answer some of your 
questions:

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There have been a number of threads in both the WINNT and WIN32
forums about the up-coming second release of the Win32 Preliminary
SDK and the first Windows NT 3.1 beta.  We are in the final stages of
testing these releases now and wanted to make sure we gave you the
most accurate information as soon as it was available.

The second release of the SDK will be ready before the end of October
and will be sent directly to all registered owners of the first
release.  (We've just mailed a letter to all registered owners for
address confirmation.  If you don't receive the letter in the next
two weeks, please call the Microsoft Developer Services Team at
800-227-4679.)  This release will include the Win32s libraries, adds
the Windows NT features not enabled in the July release (better NTFS
and multimedia support, POSIX, etc.), and has reduced size and
improved performance.

At the same time, we will release a beta version of the operating
system for end users.  We will begin with a few thousand beta sites
and expand that over time.  We will ship the retail release of
Windows NT when feedback from these beta sites indicates that it
meets our standards and comittment to high quality.  Based on the
latest information and our determination to ensure that the final
code is of very high quality, the final release of Windows NT will be
in early 1993, not end of 1992, as previously anticipated.

The Windows NT 3.1 Product Team