I tried this under Python 2.3.3, 2.5.1 (native) and 2.3.4 (cygwin).  The
operating system is Windows 2000 SP4.

C:\Python23>python
Python 2.3.3 (#51, Dec 18 2003, 20:22:39) [MSC v.1200 32 bit (Intel)] on
win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import os.path
>>> print os.path.exists('nul')
True

C:\Python25>python
Python 2.5.1 (r251:54863, Apr 18 2007, 08:51:08) [MSC v.1310 32 bit
(Intel)] on
win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import os.path
>>> print os.path.exists('nul')
False

$ python
Python 2.3.4 (#1, Jun 13 2004, 11:21:03)
[GCC 3.3.1 (cygming special)] on cygwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import os.path
>>> print os.path.exists('nul')
True

So there does seem to be a change in behaviour at 2.5.