As noted on the download page
"*Known Installation Problem:* The wordnet distribution
/path/to/your/nltk_data/corpora/wordnet.zip needs to be unzipped before
it can be used accessed from NLTK."
The first examples in the NLTK book use corpora, so why not A.
distribute it unzipped. B. Change the installation instructions to
remind you to do it first. It's kind of a buzzkill to have the initial
example in the book fail.