Free Download of Windows 7 Release Candidate

Welcome to Windows 7 Release Candidate (RC) testing. We're on our way to Windows 7, and if you like trying out pre-release software, now’s your chance. You get to see what's coming, and we get to see if our changes and fixes from the Beta testing are working correctly.
How do you test the software? You put it on your PC, and then do what you'd normally do. Your PC will automatically and anonymously send our engineers the information they need to verify the fixes and changes they made based on the Windows 7 Beta tests.

http://www.microsoft.com/windows/windows-7/download.aspx