This is essentially the same as asking how to detect that I am running under a 64-bit version of Windows.
os.name
gives 'nt' under both win7 64 and winXP 32 (my two available test computers).
sys.platform
gives 'win32' in both of those cases.
It looks like the only thing I've found so far that works is to check the registry key HKLM\HARDWARE\DESCRIPTION\System\CentralProcessor\0\Identifier
and if 'x86' doesn't appear in it, assume that means 64-bit windows. Is that reliable?
(the python process needs to run under python 2.7 32-bit)