Today at BUILD Conference, Microsoft showcased a detailed preview of the next major release of Windows, code-named “Windows 8”. You can now download the Windows Developer Preview. Windows Developer Preview is a pre-beta version of Windows 8 for developers.
Windows Developer Preview works great on the same hardware that powers Windows Vista and Windows 7:
Note: Windows Developer Preview is not stable, operate correctly or work the way the final version of the software will. It should not be used in a production environment.
Download link doesn't work for 64-bit (without developer tools)