...This is the movie version of the song. For the intro verse "This is it!(etc)" 
instead of the noodling/riffing, I've subbed in the same chords used in the verse 
parts. I worked this song out on an acoustic guitar, so the chords worked best -- 
I just sort of finger-pick a little to get that noodley feel. And, since a BUNCH 
of lines of this little ditty are "na-na" and "la la" and YODELLING, I've tried to 
phonetically and rhythmically transcribe them as best as I possibly could have. 
*note: I play the Bm as a barre chord, and the 'sliding' up part is the best I 
could decipher tonally.
       
 
        E (022100@1)            AThis (x02220@1)is it, this is the place
  
             D (xx0232@1)                     AThese (x02220@1)truffula trees are just a-what I need 
    
      E        (slide E up to the 4th, then 6th fret for "down" & "thneed")
Gonna chop one down and make my thneed

-- But first!

E (022100@1)               A (x02220@1)       D (xx0232@1)  A (x02220@1)
Na na nana-na-na, nana-nana nana-na, now you!

E (022100@1)               A (x02220@1)       D (xx0232@1)  A (x02220@1)Na na nana-na-na, nana-nana nana-na (that's great)

E (022100@1)               A (x02220@1)       D (xx0232@1)  A (x02220@1)La-la lala-lala, la-la-la lalala-lalala

E (022100@1)               A (x02220@1)       D (xx0232@1)  A (x02220@1)Haaaaa-ahaha, hoobahoobahoobawow wahooba how-how

G (320003@1)        A (x02220@1)            D (xx0232@1)    Bm (x24432@1)So now our friendship can begin, hand in hand and wing and fin

G (320003@1)              A (x02220@1)            D (xx0232@1)    Bm (x24432@1)There's nothing you and I can't do, so lets all make my dreams come

E (022100@1)                 A (x02220@1)       D (xx0232@1)          ATruuuuue-a-yodeloo, (x02220@1)a-yodeloo a-yodelayhee-hehoo

(Continue yodelling and repeat chords x 2 more times)

-- Hey guys? C'mon, where's my back-up chorus?