Try
XP Codec Pack 2.0.7.1, it's the one I use and I rarely have trouble playing files. Be sure to install it after you d/load it. Google codec to find info on them.
Also try
VLC media player, it has the codecs built in and is very reliable. I keep it on hand just for files that won't play right in WMP. It's a good back up for other players.
More info:
http://www.gnutellaforums.com/tips-t...p3-fixers.html