NIF is a popular file format used by 3D games such as Morrowind, Oblivion, Fallout 3, Civilization IV, and many more. The Blender NIF scripts enable you to read and write files that are compatible with these games in Blender.
The windows installer updated for Python 2.6 and PyFFI 2.0.1, besides some other minor enhancements (see changelog for details).
You can grab the latest version of the scripts here:
https://sourceforge.net/projects/niftools/files/
For more documentation and help with the scripts, visit the wiki or the forum:
http://niftools.sourceforge.net/wiki/Blender
http://niftools.sourceforge.net/forum