When you want to play the songs with windows media player go to Extra - Options - File Types Select all. Now your music should be played wit wmp11 as default.
Windows media player is not the best media player. Most people use it, because it is part of WindXp or Vista.
For music I would use WinAmp. For me the best there is.
It plays also video's, but i would recommend Gomplayer. It plays all file types and is free. No need to download extra codecs. Just go to preferences -- Others -- select
All File Types and Codecs.
http://www.winamp.com/player/
http://gom-player.en.softonic.com/