--with-python under MacOSX

When I try to build PostgreSQL configured using the --with-python flag,
the build ends with the statement:

*** Cannot build PL/Python because libpython is not a shared library.
*** You might have to rebuild your Python installation. Refer to
*** the documentation for details.

Unfortunately, I can't find the documentation it is refering to. I've
tried rebuilding Python a couple of different ways, but I never seem to
get a libpython*.so (I do get libpython*.a's). I can find any reference
to libpython in the PostgreSQL docs. I expect I'm in a weird case since
I'm trying to get all of this working under MacOSX.

Any suggestions?

Thanks,
-Nathan