Too broke to buy a copy of Windows? Too impatient to wait for the next release?
It looks like the Microsoft team is giving out free copies of Windows 7 Ultimate to people willing to beta test it. They seem lenient on the requirements. Here's the announcement and the link to the Windows team blog:
To show our appreciation, members of the invitation-only Windows 7 Technical Beta Program will be eligible for a free, final copy of Windows 7 Ultimate. For more information on how to take advantage of this, refer to Paul’s post in the .Beta_Program newsgroup for details.
Showing Our Thanks to Windows 7 Beta Testers…. - Windows 7 Team Blog - The Windows Blog