This amazing song has been played acousticly many different ways.
the basic acoustic progression is shown here.


E  --------------------------------------------------------
B  -----1-------1--------1-----1-----1-----1-----0-----0---
G  ---------0---------------------------------0-----0------
D  ------------------3------3-----0-----0------------------
A  --0-----------------------------------------------------
E  --------------------------------------------------------


after playing this a whole bunch ofg times (depending on the version
of the song)  then break into the chords which are  Am F Dm G Am F G.

this my not be totally accurate, i'm not sure about the notes on F
notes (3rd fret 4th string)
post any corrections on here.