Although the active version of python on my machine is 2.5.2 and I have
never had an alpha version installed, crash reports for python report
the version as "2.5a0 (2.5alpha0)".

Version details: active version of python is from the current python.org
dmg download for Mac OS X 10.4 i.e. the universal framework build. When
starting python, I get:

Python 2.5.2 (r252:60911, Feb 22 2008, 07:57:53) 
[GCC 4.0.1 (Apple Computer, Inc. build 5363)] on darwin
Type "help", "copyright", "credits" or "license" for more information.

but in crash reports, I get:

Command: Python
Path:   
/Library/Frameworks/Python.framework/Versions/2.5/Resources/Python.app/Contents/MacOS/Python
Parent:  bash [27154]

Version: 2.5a0 (2.5alpha0)

and python is given as version 2.5a0 in the binary image listing which
follows.

Darwin Kernel Version 8.11.0: Wed Oct 10 18:26:00 PDT 2007;
root:xnu-792.24.17~1/RELEASE_PPC

I think I did have 2.5.1 installed prior to installing 2.5.2 and I also
have two older versions of python installed - 2.4 (also the python.org
build) and 2.3 (as pre-installed by Apple) - but I never installed 2.5.0
or any version/candidate in the 2.5 line prior to 2.5.1.

I'm not sure what further information might be helpful but would be
happy to provide it on request.