John Williams
c/o The Gorfaine/Schwartz Agency, Inc.
4111 W ALAMEDA AVE STE 509
BURBANK CA 91505-4140

I want to be a film composer. What advice can you offer me?
Unfortunately, not much. However, you might find this article from filmscoremonthly.com of interest.

What is the chorus singing in The Phantom Menace?
Williams used two lines from Robert Graves' poem "Battle of the Trees" — "Under the tongue root a fight most dread, and another raging, behind, in the head" — which he had translated into several languages and chose Sanskrit because he liked the way it sounded. He didn't use all the words, just selected ones. Here is the Sanskrit transliteration:

Korah Matah Korah Rahtahmah
Korah Rahtamah Yoodhah Korah
Korah Syahdho Rahtahmah Daanyah
Korah Keelah Daanyah
Nyohah Keelah Korah Rahtahmah
Syadho Keelah Korah Rahtahmah
Korah Daanyah Korah Rahtahmah
Korah Daanyah Korah Rahtahmah
Nyohah Keelah Korah Rahtahmah
Syadho Keelah Korah Rahtahmah
Korah
Korah Matah Korah Rahtahmah
Korah Daanyah Korah Rahtahmah
Nyohah Keelah Korah Rahtahmah
Syadho Keelah Korah Rahtahmah
Korah

Madhurah swehpna, go rahdomah swehpna,
Madhurah swehpna, go rahdomah swehpna,
Mooritioo, madhurah swehpna.

Did John Williams compose a piano duet for Road to Perdition?
Not the same John Williams.  That was a Chicago-based accordionist John Williams.  See www.johnwilliamsmusic.com for further information.