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.

To use KML2Shapefile, download and install MapWindow GIS, and then KML2Shapefile.  Activate it through the MapWindow 'Plug-ins' tab