VLC will do fine. http://www.videolan.org/vlc/ (choose nearest mirror site) It's free & has built-in codecs. The controls are a bit basic but it does the job & has the newest codecws for translating the newest formats. You might also like to see this: Setting Default video app

If you insist on WMV files then you'd need xtra codecs: A. http://www.land.ee/d_nimo_codec.html or B. http://www.free-codecs.com/ for use with WMP.