what codec are you downloading???? and for what ???? you'll only maybe need codec to play the file when you've downloaded but you question doesnt seem to relate to that.
have you got "bittorrent" or "bittornado" downloaded and installed???
if you've downloaded the file and are having trouble playing it i can understand,i use nero vision express 2 and it seems to play most things...another great player is windows media player classic which plays quicktime and shit without having download anything else......
"""WITH BITTORNADO/BITTORENT INSTALLED"""
(1)click the on the file ,ie "Gina_W.avi.*******" (AT TOP LEFT OF FILE PAGE) then bittotornado starts automatically,select what folder to download to and voile.
if worst comes to worse ,read the FAQ and you should be able to work most problems out!