NLTK is…
To download nltk:
pip install NLTK
Once the NLTK module is downloaded you can check that it has been downloaded by opening the python shell and typing: import NLTK
To download the files related to NLTK:
import nltk nltk.download()
There will be a dialog box that pops up and you will want to download all. Once that is complete you will be able to get started with NLTK.