This error happens when opting in for compiling the scripts at
installation. (please note also that I did not selected "register
extension", but I don't think this has an impact).

Here is the text from event viewer:

Product: Python 3.0rc3 -- Error 1722. There is a problem with this
Windows Installer package. A program run as part of the setup did not
finish as expected. Contact your support personnel or package vendor. 
Action CompilePyc, location: L:\Python30\python.exe, command: -Wi
"L:\Python30\Lib\compileall.py" -f -x
bad_coding|badsyntax|site-packages|py2_ "L:\Python30\Lib" 

Running the command manually indeed crashes, because of pipe symbol
being interpretted at shell level, not Python.

Please find attached a patch on Tools\msi\msi.py that addresses the
problem (untested, I don't have VStudio )