python Lookup Error

import nltk.data

text = "Punkt knows that the periods in Mr. Smith and Johann S. Bach do not mark sentence boundaries.  And sometimes sentences can start with non-capitalize words.  i is a good variable name."

tokenizer = nltk.data.load('tokenizers/punkt/english.pickle')

print '\n-----\n'.join(tokenizer.tokenize(text.strip()))

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$ python nltkexample.py
Traceback (most recent call last):
  File "nltkexample.py", line 5, in <module>
    tokenizer = nltk.data.load('tokenizers/punkt/english.pickle')
  File "/usr/local/lib/python2.6/dist-packages/nltk-2.0b9-py2.6.egg/nltk/data.py", line 594, in load
    resource_val = pickle.load(_open(resource_url))
  File "/usr/local/lib/python2.6/dist-packages/nltk-2.0b9-py2.6.egg/nltk/data.py", line 673, in _open
    return find(path).open()
  File "/usr/local/lib/python2.6/dist-packages/nltk-2.0b9-py2.6.egg/nltk/data.py", line 455, in find
    raise LookupError(resource_not_found)
LookupError: 
**********************************************************************
  Resource 'tokenizers/punkt/english.pickle' not found.  Please
  use the NLTK Downloader to obtain the resource: >>>
  nltk.download().
  Searched in:
    - '/home/xralf/nltk_data'
    - '/usr/share/nltk_data'
    - '/usr/local/share/nltk_data'
    - '/usr/lib/nltk_data'
    - '/usr/local/lib/nltk_data'
**********************************************************************

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