Today a build of Windows Server 2008 R2 SP1/Windows 7 SP1 leaked to the internet, so I grabbed a copy & installed it in a fresh Windows 7 install on a VPC.
File name: 7601.16537.100327-0053_Update_Sp_Wave0-B1SP1.0_DVD.iso
It took approximately 14 minutes to complete the install & I experienced no glitches.
Here are a few screenshots
First Install Screen
Install Completed Successfully
About Windows

What it contains, brief description of the KB List (excel format)

Edit: I removed the (Pre Beta) from the subject line.








