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I am expereincing the problem described by the original
poster.  I undertand that MSVC8 is not officially supported,
and I'm trying anyway.

I downloaded the 2.5.0 final tarball and began working in
the PCbuild8 directory.

Firts off, I found that I had to build two projects before
pythoncore would build: 

  make_versioninfo
  make_buildinfo

When I tried to build pythoncore, I got the linker error
saying that _init_types could not be found.  So I added
_typesmodule.c to the pythoncore project.  Finally,
pythoncore built cleanly.

Next up, I wanted to build pythoncore_pgo.  So I added 
_typesmodule to this project also.  But try as I might,
every attempt to build pythoncore_pgo produces the link
error on _init_types.  (I also did a 'clean' on pythoncore
just to be safe.)

I do not understand this.  Unlike the original poster, I
have not modified any source.  It seems like the definition
of pyMODINIT_FUNC as extern "C" void might be involved, but
I agree with gbrandl that the static int in Python-ast.c is
not the issue, because that is a different scope.  

So the linkage problem with pythoncore_pgo remains a mystery
to me.  I hope someone has more clues than me.