Test whether Python 2.0 or greater is installed by typing python at the command line. If Python hasn't been installed, download and install it from http://www.python.org.
Download and install WordNet 2.0 from http://www.cogsci.princeton.edu/~wn/.
Download PyWordNet from http://sourceforge.net/projects/pywordnet.
(Windows) Run pywordnet.exe.
(Other operating systems) Unpack PyWordNet. In the directory that contains the unpacked files, type python setup.py install at the command line.
Type python at the command line, and try the examples.