I use both WinAmp and WMP without any problems. I've installed a few "codecs packs" and my WMP plays about everything I feed it with.
Entreri.
p.s. You can try installing Microsoft's codecs :
http://download.microsoft.com/downlo.../WM9Codecs.exe
If you decide to try one of the many codec packs out there, some of them install spywares so you may have to clean up after installing them.