Natural Language Processing in Python
engineroom.trackmaven.com
engineroom.trackmaven.com
That being said, a lot of the ML, porter, and stemmer implementations are a bit out of date from the current cutting edge in the field. If you are interested in using NLTK for serious projects, I highly recommend writing custom implementations of these modules or using other libraries.
For machine learning turn to scikit-learn.
The sample uses the built-in named entity tagger but nltk also has support for leveraging the Stanford named entity tagger: http://www.nltk.org/api/nltk.tag.html#module-nltk.tag.stanfo...