I think I might know your problem now - provided you have downloaded the files properly. Try downloading the DivX codec. Head on over to
http://www.divx.com to get it - that should fix your problem.
If you're trying to play .torrent files and not .avi files, it won't work - get a bittorrent client, like BitTorrent or UTorrent, and open your torrent in them to download the files.
If it's neither of those then I'm out of ideas...