Taken from Mydigitallife:
Microsoft is scheduled to officially launch public beta of Windows 7 on January 9, 2009, which can be as soon as today. So for those who wants something more official and reliable, which has the exact same hash code for the ISO, just wait for official release.
Characteristics of Windows 7 Beta1 Build 7000 DVD ISO Image:
File Name: 7000.0.081212-1400_client_en-us_Ultimate-GB1CULXFRE_EN_DVD.ISO
Size: 3387009024 bytes (3.15 GB)
Platform: x64 (64-bit)
System Requirement: CPU: 2.0 GHz | RAM: 1 GB | HDD: 50 GB