Windows 7 Beta

Windows 7 Beta Official Page
http://technet.microsoft.com/en-us/evalcenter/dd353205.aspx

ISO image download link
- 32-Bit
http://download.microsoft.com/download/6/3/3/633118BD-6C3D-45A4-B985-F0FDFFE1B021/EN/7000.0.081212-1400_client_en-us_Ultimate-GB1CULFRE_EN_DVD.iso

- 64-Bit
http://download.microsoft.com/download/6/3/3/633118BD-6C3D-45A4-B985-F0FDFFE1B021/EN/7000.0.081212-1400_client_en-us_Ultimate-GB1CULXFRE_EN_DVD.ISO

the only difference in the url is that 64Bit has '(...CUL)X' in the middle of its iso file name.
You can test this product for 30 days without product key.

Other useful links
1. Windows 7 Team Blog
http://windowsteamblog.com/blogs/windows7/default.aspx

2. A Tour of Windows 7 Beta(PCWorld)
http://www.pcworld.com/video/id,938-page,1-bid,0/video.html