Cutting up a shapefile into smaller parts

With ogr2ogr, you can specify a bounding box that you'd like to clip by with -clipsrc x_min y_min x_max y_max, so for example, to only get the northern hemisphere of a global dataset you could do:

ogr2ogr -f "ESRI Shapefile" borders_north.shp borders.shp -clipsrc -180 0 180 90

See the ogr2ogr documentation for further options, including clipping to another geometry.

You can install and use qgis to load the file you downloaded; use the mouse or query the data for the features that you would like to select; and export the selected features to a new shapefile.

QGIS is a cross-platform (Linux, Windows, Mac) open source application with many common GIS features and functions.

A link containing tutorials that illustrates these steps in qgis is available here http://qgis.spatialthoughts.com/