So basically, if you create a playlist file in one of those formats, put it in the root of your HD, and have it reference songs on the HD itself, then it shows up in alphabetical order as a playlist in the car's interface, yeah? I think we're getting somewhere now.
Songbird might be able to help you...
http://getsongbird.com/product/
It has an add-on for exporting playlists in M3U or PLS.
http://addons.songbirdnest.com/addon/51
Songbird should be able to use the song files "in place" -- that is, it uses the library as it exists on the HD and not on your Mac. You want to do it this way, because otherwise the locations of the song files in the M3U file will not be correct.