I did the "make altinstall" rather than the "make
install" as suggested on

  http://www.python.org/download/releases/2.5/

This worked great, creating a 

  /usr/local/bin/python2.5

which doesn't clash with my /usr/bin/python. However,
it also created a

  /usr/local/bin/pydoc

which did clash with my /usr/bin/pydoc. I just removed
it and all is well. Should altinstall not create pydoc?
It could create pydoc2.5 rather than pydoc, but then
the shebang line would have to be changed to python2.5.
What about smtpd.py, idle, and python-config, which
were also created by altinstall? They don't currently
conflict with anything I have for Python 2.4, but the
potential is there for the same problem.