Python get wrong value for os.environ["ProgramFiles"] on 64bit vista

Python 2.4.3 on a Vista64 machine.

The following 2 variables are in the environment:

ProgramFiles=C:\Program Files
ProgramFiles(x86)=C:\Program Files (x86)

But when I run the following

import os
print os.environ["ProgramFiles"]
print os.environ["ProgramFiles(x86)"]

I get:

C:\Program Files (x86)
C:\Program Files (x86)

Any idea how can I get the correct value of "ProgramFiles"?