From NLTK

NLTK is hosted at GoogleCode: http://code.google.com/p/nltk/

Browse the subversion repository

http://code.google.com/p/nltk/source/browse/trunk/nltk/

Check out a copy of the repository

Point your subversion client at http://nltk.googlecode.com/svn/trunk/nltk/

Installing latest version

To install an up-to-the-minute version of NLTK, check out the subversion repository and run the setup.py script in the top directory (e.g. sudo python setup.py install; set the NLTK_DATA environment variable to point to the top level nltk_data directory.