Official Windows 7 BETA (looks like build 7000) is now available for download in 32/64-bit versions.
32 bit version: 2.44 GiB
64-bit version: 3.15 GiB
They are in limited supply, so check them out now:
I could get a BETA key for each version using Firefox 3, but no download happened. I fired up IE *shudder* and an ActiveX component was installed to download in that manner. If you are having issues, try IE!
Also, according to the installation instructions located here:
The Beta will stop working on August 1, 2009. To continue using your PC, please be prepared to reinstall a prior version of Windows or a subsequent release of Windows 7 before the expiration date. You won’t be able to upgrade from the Beta to the final retail version of Windows 7.