@Ednaelk - Sorry for being a little too late. Tom used to sing the song a capella, but since around 1980 he began singing it with the guitar.

I used to play it this way:

  Am
  Jennifer's rabbit, brown and white,
  Em
  Left the house and ran away one night 
  Am                          G
  Along with the turtle and a kangaroo 
      Em                              Am
  And seventeen monkeys from the city zoo,
      Em       Am
  And Jennifer too.
  
  
       C                               G
  They ran through the forest and they all held hands.
       Em                         Am
  They came to the ocean with the cookie crumb sands.
  C                        G
  Called it the sea of the very best dreams,
           Em                        Am
  And they all built a castle of the best moon beams.
      Em        Am
  And milky way streams.
  

However, I saw a concert video earlier this year, and discovered that Tom actually plays:

  Am
  Jennifer's rabbit, brown and white,
  G
  Left the house and ran away one night 
  Am                          G
  Along with the turtle and a kangaroo 
      E7                              Am
  And seventeen monkeys from the city zoo,
      E        Am
  And Jennifer too.
  
  
       C                               G
  They ran through the forest and they all held hands.
       E7                         Am
  They came to the ocean with the cookie crumb sands.
  C                        G
  Called it the sea of the very best dreams,
           E7                        Am
  And they all built a castle of the best moon beams.
      E         Am
  And milky way streams.
  

If I remember correctly, he put the capo on the 6th fret, which makes the song in D#m.

I think both would work well - of course the original is better, though...

Jason