Renaming the file extension isn't going to change the filetype. You have to re-encode it under a different format. Windows Media Player can still play a Windows Media Audio file if it has the file extension .fuehgir. Of course, Winamp is a bit different, but still. If you rename blah.ogg to blah.mp3, it will still be an OGG, not an MP3, because internally, it still uses the OGG format.