The release notes for Windows Virtual PC Beta has been available and can be downloaded here

Here is what the download page reads

Windows Virtual PC (Beta) is the latest Microsoft virtualization technology that allows you to run many productivity applications on a virtual Windows environment, with a single click, directly from a Windows 7-based PC.
For more information about Windows Virtual PC, please visit the Windows Virtual PC website.
The Release notes provide important information you should know prior to installing and using Windows Virtual PC, including known issues. You should familiarize yourself with all of the information prior to installing the software.

Windows Virtual PC Evaluation Guide has also been released which has detailed information about setting up and using Windows XP Mode in Windows 7.It can be downloaded from here