a m3u playlist is essentially a file that contains the paths and filenames of the mp3s it contains.
You can create it with your favorite text editor, or with your favorite music player application.
Winamp, Windows media player, foobar2000, banshee, rhythmbox are just a few examples.
But the above mentioned fireflyclient runs on Windows, Linux and OS X (it just requires java) and lets you comfortably edit and create playlists in firefly directly.
de-u/c'd NSLU2 Unslung 6.8 - mt-daapd svn-1696