I tried to install Virtual PC 2007 in Win 7 beta and the installer crashed. I followed this instruction from the Win 7 Action Center. And that did it.

Solve a problem with Windows 7 beta

An issue with the Customer Experience Improvement Program (CEIP) client in Windows 7 beta is causing Explorer and some MSI-based installers to stop working properly.

To solve this problem, follow these steps:

  1. Click the Start button , click All Programs, and then click Accessories.

  2. Right-click Command Prompt, and then click Run as administrator. In the User Account Control window, verify that Program name is Windows Command Processor, and then click Yes.

  3. In the Administrator: Command Prompt window, type or paste the following text at the prompt:

    reg delete HKLM\SOFTWARE\Microsoft\SQMClient\Windows\DisabledSessions /va /f

  4. Press Enter to install the solution.

  5. If The operation completed successfully displays, close the Administrator: Command Prompt window to complete this procedure. If "ERROR: Access is denied" displays, repeat this procedure from the top, making sure you clicked Run as administrator in step two.