If you need codecs (& it sounds like you do) see: http://www.divx-digest.com/software/nimo_pack.html (use the 2nd mirror link - the 1st seems to have moved!)

OR use a different default video player with built in codecs that plays all but the odd wmv file & is free: VLC: http://www.videolan.org/vlc/ (choose the nearest mirror site.)

And also DivX player. It's always good to have more than one player around just in case.