My understanding was that subprocess.py was supposed to be 
backwards compatible with at least Python 2.3 if not 2.2. Wanting 
subprocess and backwards compatibility, I grabbed the subprocess.py 
from 2.4b1, changed the import if so that win32api was used (since I 
had no _subprocess library!) and found several problems, of which 
this is one (one per bug report):

If the executable has a space in its path name (as is standard on 
Windows) and command-line arguments, things fail miserably:

from subprocess import *
Popen('"C:\\Program Files\\ds9\\xpaget" ds9 mode')

produces an error that C:\Program cannot be run. Clearly the double 
quoting isn't making it through Popen. Note that this runs just fine if 
there are no command line arguments, i.e. this works:

Popen('"C:\\Program Files\\ds9\\xpaget"')

Note that this same bug also exists in os.popen3, so you may have 
inherited it.

This bug does NOT occur on a unix build on MacOS X.