The .mp3 and .m3u links refer to the same mp3 file, the difference is that the .mp3 link is meant for downloading of the mp3 file, while the .m3u link is meant for streaming (i.e. the mp3 player should start playing before downloading the whole file) the mp3 file to your software mp3 player (e.g. WinAmp for Windows, xmms for Unix, or iTune for Mac).