Why try WMP??? Use other interesting players like WinAmp and VLC, Real(obviously real requires a license)............
About the plug-ins required directly install the Codec Packages supported by wmp11(freeware) in case it asks for unknown file type.
Else install the required plug ins for wmp11 and not for wmp9.
Note that wmp detects what music you play(i.e) checks whether you've purchased or not and so, i do not recommend wmp for the music file you play.