a .torrent file is a a piece of info that you download of a tracker site such as torrentspy.com. This isnt the actually file but info telling the applaction such as utorrent or bitlord what files to download off other people. Then the app downloads tiny pieces off many diffent people at once. You can get very high download speeds ( i have gotten 500kbs)and a lot of large files can be downloaded such as movies tv shows and games. As far as the orignal quesion i recommend this site
http://www.portforward.com/routers.htm