The other version seems fairly off, so here's the real deal:

The song's in Fm, so just put a capo on the first fret 
and play in the key of Em, just like the guy (or girl) who played 
this on the recording. 
Or tune the guitar up one half step. 
To view the simpler chords just select "Transpose Down 1 Half Step" on the upper 
right area of this page.

     Fm           
Come gather 'round children,
     Eb
It's high time ye learned,
        Fm   
'Bout a hero named Homer
      Eb          Fm
And a devil named Burns.


Fm
We'll march till we drop,
    Eb
The girls and the fellas,
      Fm
We'll fight till the death
        Eb        Fm
Or else fold like umbrellas.

         Ab                 
So we'll march day and night,
       Eb
By the big cooling tower,
Fm             
They have the plant,
    Eb          Fm    (last time last chord is Bb, not Fm)
But we have the power.

Ends in Fm.

P.s. if you have capo 1st fret play the now 2nd fret on the low E-string 
right before the chorus (sounding tone is G).


Now do "Classical Gas"!