KML2Shapefile is a plugin to MapWindow GIS that converts Google Earth KML and KMZ files into shapefiles for use in a GIS.

KML2Shapefile will split each KML geometry type into a separate shapefile.  It supports complex geometries, and is able to present much of the KML as attribute data.

 Download KML2Shapefile  and install it into the MapWindow Plugins folder.  Activate it through the MapWindow 'Plug-ins' tab