I just found this really great audio player called foobar 2000 that can play pretty much any song file format. I have tried it with .m4a, mp3, wma, and wav, but I think it also plays ogg and some others. You can download it here: http://www.foobar2000.org/download.html
Yeah Foobar is a pretty good tool to have. It is also very handy when you want to make a gapless Audio CD from MP3 files. You can use Foobar with Nero to do this. Also WinAmp is by far the best player to play audio files on. Exact Audio Copy is the best programme to rip CD's to MP3's on. Tag & Rename is the best tagging programme.