There's lots of palm muting and sometimes ringing out just listen for the changes.
Also when Brett plays C and Am sometimes he drops his pinkie on the third fret of the B 
He does this in the outro and in between verses.
Like so:
       C      Am
E ----0-0-----0-0--------- | 
B ----1-3-----1-3--------- | 
G ----0-0-----2-2--------- | 
D ----2-2-----2-2--------- | 
A ----3-3-----0-0--------- | 
E ----x-x------x-x-------- | 

Hope I could explain that well enough. Anyway it's a really fun song with awesome 
Hope you enjoy!

C
Tired muscles, tired eyes
Am
Can't sleep through this Oaxacan night
Em
He's kept away from dreaming, haunted by thoughts of failing
C
The family whom he shares a bed
Am
A tiny room even less bread
Em
He cries out to himself silently
            C      Am                        Em
I am not a man                no I am not a man
           C                         Am
I am not a man  I can't feed my children
                      Em
This is no life for them

C Am Em

C
So he's out of bed with the sunrise
Am
He kisses his wife and kids goodbye
Em
Then heads north to the border To work, become a provider
C
But gathered at the country line
Am
Are protesters all holding signs
Em
He can't read but translates perfectly

             C         Am                 Em
I am not a man              No I am not a man
               C                  Am
No I am not a man I'm just a Mexican
Em
Illegal immigrant

Dm
The politicians the pundits the public debate
Am        G                   F
But one question's lost in policy
Am                                              C
"Is a man not a man if he's born outside a boundary?"
Dm
Stumbling through the desert alone and afraid
Am        G             F
He almost dies from the heat
G
But he thinks of his family and that keeps him going
F
He won't stop for death least the laws of a country G
Arrested is no threat
                              F
when you're already living unfree

Unfree!

C
So he works the fields from 5 to 9
Am
Plus any job that he can find
Em
Saves up all his money, sends it to his family
C
Before he falls asleep at night
Am
A thousand miles from his life
Em
He assuredly repeats

          C       Am                     Em
I am a human                Yeah I am a human
              C                 Am
Yeah I am a human a father a husband
             Em
A global citizen

C Am Em

                      C               Am      Em
Not a debatable statistic
                           C          Am        Em
I'm not your problem economic
                           C          Am
I'm not a threat to patriotic
            Em
That's idiotic
     C
I Am A...