After installing the latest graphviz (2.26.3) on my Windows 7 Ultimate 64bit, I receive the following error:
C:>easy_install pygraphviz Searching fo
PyGraphviz uses an C language extension module (generated by SWIG). So you need a compiler to build the extension. You might need the same compiler that built your Python executable.
There is some information in this question Building Python C extension modules for Windows
and also at http://www.swig.org/Doc1.3/Python.html#Python_nn12