*.ogg files are audio files...and not just audio files, it's the format of the future. Ogg files are encoded in the Vorbis format, which is a completely copyright free format (unlike mp3 on which FhG still has a patent) and they're comprarable in quality to mp3, if you encode it at a decent bitrate.

Website:
http://www.vorbis.com/index.psp

Winamp plugin:
http://www.blorp.com/~peter/zips/in_vorbis.exe

Once you've installed the winamp plugin, select 'disk writer' as the output plugin in winamp, and start the file. You'll get a *.wav file which you can turn into an mp3 the normal way.