Python: get windows OS version and architecture

First of all, I don't think this question is a duplicate of
Detect 64bit OS (windows) in Python
because imho it has not been thoroughly answered.

The only approaching answer is:

Use sys.getwindowsversion() or the existence of PROGRAMFILES(X86) (if 'PROGRAMFILES(X86)' in os.environ)

But:

• Does the windows environment variable PROGRAMFILES(X86) reliable? I fear that anyone can create it, even if it's not present on the system.
• How to use sys.getwindowsversion() in order to get the architecture?

Regarding sys.getwindowsversion():
The link http://docs.python.org/library/sys.html#sys.getwindowsversion
leads us to http://msdn.microsoft.com/en-us/library/ms724451%28VS.85%29.aspx
but I don't see anything related to the architecture (32bit/64bit).
Moreover, the platform element in the returned tuple seems to be independent of the architecture.

One last note: I'm looking for a solution using both python 2.5 and a windows version starting at Windows XP

Thanks!

Edit:
The relevant info is available here
http://msdn.microsoft.com/en-us/library/ms724340%28v=VS.85%29.aspx
but how can I get this with python?

Edit2: On a 64bit windows, with a 32bit python interpreter:

• os.environ["PROCESSOR_ARCHITECTURE"] returns
  • 'x86'
• platform.architecture() returns
  • ('32bit', 'WindowsPE')