I have gmplayer and mplayer installed (via pacman), along with codecs-20050115-1. Shouldn't this be enough to view .wmv files? I can't seem to view them at all.
I think that it would be enough. I can play .wmv files with mplayer without any problem.
Are the files that doesn't play protected for copyright? I had an issue with .wma files from online music sites that wouldn't play with mplayer.
You can try to play them in another player like xine.