Hi,
If you have a .mid file of the song, then either Notation Musician or Notation Composer (
www.notation.com/NotationMusician.php or
www.notation.com/NotationComposer.php) can give you chord names for the song file.
If you're talking about an audio file, I'll have to bow out to more informed folks
I typically sit down with my guitar and hammer it out that way.
ttfn,
Sherry