Although Python 3.0 is now available, many packages that NLTK requires do not have distributions for Python 3.0. For now you should use NLTK with Python 2.4.*, 2.5.*, or 2.6.* only. Windows You will need to obtain the following packages and install them on your computer using an administrator account: Python: http://www.python.org/ftp/python/2.6.4/python-2.6.4.msi PyYAML: http://pyyaml.org/downl