Help regarding NER in NLTK
Training a model, related to information extraction, in general, and named entity recognition/resolution (NER), in particular, is described in detail in Chapter 7 of the NLTK Book, available online at this URL: http://www.nltk.org/book/ch07.html.

Additionally, I think that you might find useful my related answer on Cross Validated site. It has a lot of references to relevant sources on NER and related topics as well as to various related software tools.