The Microsoft Windows 7 Beta will be available to download in 32/64-bit version via the Windows 7 page starting January 9th PST for a limited time to the first 2.5 million people who download the beta.
Please keep in mind that this Beta version is set to expire on August 1st, 2009.
Read Windows 7 Beta Boasts Sub-30 Second Boot Time
Read Windows 7 Beta: First Impressions