os.environ["PROCESSOR_ARCHITEW6432"] will tell you the true underlying processor architecture when under WOW. Therefore, if you find that this variable exists, you are under WOW.

Example, on my 64-bit machine with a 32-bit compiled Python:

Python 3.1.2 (r312:79149, Mar 21 2010, 00:41:52) [MSC v.1500 32 bit (Intel)] on
win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import os
>>> os.environ["PROCESSOR_ARCHITECTURE"]
'x86'
>>> os.environ["PROCESSOR_ARCHITEW6432"]
'AMD64'