most videos made by national geographic are available at their web site. however, they are mostly 3-5 mins clips. if you need the whole videos, you might want to torrent them. one of the best site to find torrent files is : mininova.org. but, if it (the desired video) is not available there, just google it in the format "<<video name>> torrent". you'll need a torrent client such as bittorrent. most files are found in .rar or as-is. i'd always run a virus check on any downloads, just to make sure. i have downloaded a lot of such videos, mostly produced by bbc. haven't had much luck with all national geographic videos.

Good Luck.

peace and enjoy.