The version I've tried:
 * bzr 1.12-1 Windown Standalone Installer, MD5: 7461cf50c630b559a2dd9f6c20a63a82

when run bzr --version:
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Bazaar (bzr) 1.12
  Python interpreter: D:\usr\local\Bazaar\python25.dll 2.5.2
  Python standard library: D:\usr\local\Bazaar\lib\library.zip
  bzrlib: D:\usr\local\Bazaar\lib\library.zip\bzrlib
  Bazaar configuration: D:\Documents and Settings\ntt6\Dados de aplicativos\bazaar\2.0
  Bazaar log file: D:\Documents and Settings\ntt6\Meus documentos\.bzr.log

Copyright 2005, 2006, 2007, 2008, 2009 Canonical Ltd.
http://bazaar-vcs.org/

bzr comes with ABSOLUTELY NO WARRANTY.  bzr is free software, and
you may use, modify and redistribute it under the terms of the GNU
General Public License version 2 or later.
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So, I've tried to run the command:
 * bzr help commands

And Bazaar raised the error:
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bzr: ERROR: exceptions.ImportError: Unable to load subvertpy extensions - did you build it?

Traceback (most recent call last):
  File "bzrlib\commands.pyo", line 896, in run_bzr_catch_errors
  File "bzrlib\commands.pyo", line 842, in run_bzr
  File "bzrlib\commands.pyo", line 542, in run_argv_aliases
  File "bzrlib\commands.pyo", line 856, in ignore_pipe
  File "bzrlib\builtins.pyo", line 3666, in run
  File "bzrlib\help.pyo", line 51, in help
  File "bzrlib\help_topics\__init__.pyo", line 826, in get_help_text
  File "bzrlib\help_topics\__init__.pyo", line 90, in get_detail
  File "bzrlib\help.pyo", line 78, in _help_commands_to_text
  File "bzrlib\help.pyo", line 77, in <genexpr>
  File "bzrlib\commands.pyo", line 173, in get_cmd_object
  File "bzrlib\commands.pyo", line 190, in _get_cmd_object
  File "bzrlib\registry.pyo", line 168, in get
  File "bzrlib\registry.pyo", line 61, in get_obj
  File "bzrlib\registry.pyo", line 66, in _do_import
  File "D:/usr/local/Bazaar/plugins\svn\mapping3\__init__.py", line 25, in <module>
  File "subvertpy\__init__.pyo", line 97, in <module>
ImportError: Unable to load subvertpy extensions - did you build it?

bzr 1.12 on python 2.5.2 (win32)
arguments: ['bzr', 'help', 'commands']
encoding: 'cp1252', fsenc: 'mbcs', lang: None
plugins:
  bzrtools             D:\usr\local\Bazaar\plugins\bzrtools [1.12]
  launchpad            D:\usr\local\Bazaar\plugins\launchpad [unknown]
  netrc_credential_store D:\usr\local\Bazaar\plugins\netrc_credential_store [unknown]
  qbzr                 D:\usr\local\Bazaar\plugins\qbzr [0.9.8]
  svn                  D:\usr\local\Bazaar\plugins\svn [0.5]
  xmloutput            D:\usr\local\Bazaar\plugins\xmloutput [0.8.1]
*** Bazaar has encountered an internal error.
    Please report a bug at https://bugs.launchpad.net/bzr/+filebug
    including this traceback, and a description of what you
    were doing when the error occurred.
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