NTLM authentication in Python

I'm trying to implement NTLM authentication on IIS (Windows Server 2003) from Windows 7 with python. LAN Manager Authentication Level: Send NTLM response only.
Client machine and server are in the same domain.
Domain controller (AD) is on another server (also running Windows Server 2003).

I receive 401.1 - Unauthorized: Access is denied due to invalid credentials. Could you please help me find out what is wrong with this code and/or show me the other possible directions to solve this problem (using NTLM or Kerberos)?

import sys, httplib, base64, string
import urllib2
import win32api
import sspi 
import pywintypes
import socket

class WindoewNtlmMessageGenerator:
    def __init__(self,user=None):
        import win32api,sspi
        if not user:
            user = win32api.GetUserName()
        self.sspi_client = sspi.ClientAuth("NTLM",user)   

    def create_auth_req(self):
        import pywintypes
        output_buffer = None
        error_msg = None
        try:
            error_msg, output_buffer = self.sspi_client.authorize(None)            
        except pywintypes.error:
            return None
        auth_req = output_buffer[0].Buffer
        auth_req = base64.encodestring(auth_req)
        auth_req = string.replace(auth_req,'\012','')
        return auth_req 

    def create_challenge_response(self,challenge):
        import pywintypes
        output_buffer = None
        input_buffer = challenge
        error_msg = None        
        try:
            error_msg, output_buffer = self.sspi_client.authorize(input_buffer)
        except pywintypes.error:
            return None
        response_msg = output_buffer[0].Buffer       
        response_msg = base64.encodestring(response_msg)
        response_msg = string.replace(response_msg,'\012','')
        return response_msg 


fname='request.xml'
request = file(fname).read()
ip_host = '10.0.3.112'

ntlm_gen = WindoewNtlmMessageGenerator()
auth_req_msg = ntlm_gen.create_