I went to the sticky on Codecs, and it said I should use GSpot to figure out what codec I need to play a file. I opened up Naruto 151, and under stat, it said that it was "Not a valid AVI File". I clicked on that, and it said "This is, or appears to be, an unsupported filetype. GSpot provides full support for AVI and OGG media streams. Based on its composition, GSpot believes the filetype to be "Non-AVI File - Type Unknown.".
I tried downloading the CCCP, but that still didn't make it work. The player I usually use is Windows Media Player, but that didn't work, so I tried QuickTime and DivX (now uninstalled), but those didn't work either. I have no idea what to do.