The above suggestion isn't all that good since you might find yourself with a bunch of conflicting codecs, a situation which isn't all that good in.
I personally suggest using either
VLC or
Mplayer (click on the links) which are free players that need no additional codecs to play most of the audio/video formats out there.
If you insist on using Windows Media Player, then I suggest the CCCP:
http://www.kickassanime.org/wiki/ind...?title=Compack
Quote from ShinL:
"The suggested procedure is:
1. check the FAQ before installing the pack on an OS that is not supported. The FAQ contains information on supported systems.
2. uninstall everything playback-related software you installed yourself (even CCCP if you encountered trouble with playback before reading these basic instructions). to check whether you are free of any of the more popular codec packs, use the new tool "CCCP Insurgent" (cccpi.exe)
3. reboot
4. install CCCP (check for updates every now and then)
5. reboot (you might get away without the reboot; see if the installer asks for it)
6. play file "