Videolan can now play WMV9: http://nanocrew.net/?p=129, but more interesting is that the documents for decoding VC-1 (which is under a fee) is free for a trial period which should make it possible for making a media-decoder for Haiku.
http://www.smpte-vc1.org/TestMaterials.html
More info here:
http://nanocrew.net/?p=126