ImportError: No module named bdiff

[TK Soh]

I tried to tap into Mercurial 0.9.4's library installed by berkwood's
win32 installer with the following script but got an error on bdiff:

    ---------------------
    import sys
    sys.path.append(r'c:\mercurial\library.zip')

    from mercurial import hg
    -----------------------------

Here's the error message:
:
    D:\>python hglibtry.py
    Traceback (most recent call last):
      File "hglibtry.py", line 4, in ?
        from mercurial import hg
      File "mercurial\hg.pyc", line 12, in ?
      File "mercurial\localrepo.pyc", line 11, in ?
      File "mercurial\changelog.pyc", line 8, in ?
      File "mercurial\revlog.pyc", line 15, in ?
      File "mercurial\mdiff.pyc", line 8, in ?
    ImportError: No module named bdiff

Is it legal to do so? What went wrong?

Thanks.