You need to install the correct codecsfor WMP or you can get VLC media player as it has all the codecs already installed and its a free download these are the links you will need...

http://www.xpcodecpack.com/ this one if you use XP

http://www.videolan.org/vlc/ this one for the VLC media player

And this thread will explain about different codecs and players...
http://www.gnutellaforums.com/showth...threadid=40665