http://mediacoder.sourceforge.net/

MediaCoder is a free audio/video batch transcoder, putting together many excellent audio/video softwares from the open source community into one friendly GUI. On video side, MEncoder is used as back-end, which provides support for nearly all known video compression and container formats as well as rich and useful video filtering features (e.g. post-processing, 3D de-noise). On audio side, MPlayer and Winamp input plugins used as decoders, various encoders integrated, MediaCoder can simply batch transcode among any known audio formats, with tags transferred, file names generated, and even performing audio filtering (e.g. resample, normalize) on the fly.

MediaCoder, converts almost everything

If you only want to play it on your pc, just get the plugin for Winamp/WMP. If you're using foobar2000, it's supported natively.

http://mediacoder.sourceforge.net/