Steps to reproduce:

1. python-2.7.2.msi /qb
2. Check registry for HKLM\SOFTWARE\Python or HKLM\SOFTWARE\Wow6432Node\Python

Expected behavior:
The key will exist and contain a key for 2.7 providing information such as the installation path.

Observed behavior:
The key and its subkeys are not created at all.

Workaround:
Don't use the /passive, /quiet, or /qX options. 

Additional information:
* Running msiexec /fm python-2.7.2.msi does not insert the missing registry entries.
* Running python-2.7.2.msi without options after install and choosing repair /also/ fails to insert the missing registry entries.
* Aside from inserting the entries by hand, uninstalling and re-installing with the interactive GUI seems to be the only way to populate them.

I've tested this on 64bit Windows 7 with 32bit Python 2.7.2 msi package only.

There is an old bug report against 2.5 which dealt with a very similar problem, maybe the answers are the same?

http://bugs.python.org/issue4567

Basically the location in the registry has changed from HKLM to HKCU. Here is the last message in the thread directly:

http://bugs.python.org/msg78058

Joe: this is indeed likely the explanation.

Paul: can you confirm?
Also: try adding "ALLUSERS=1" to the msiexec command line.