Original score is pretty rarely used in trailers. It happens, but usually trailers use bits from other scores or other music.
> Im sure that, when I watched the trailer for 'Alamo', a large portion of
> the background music was from 'Gladiator' soundtrack, at the beginning of
> the track: 'The Battle'. Am I wrong by thinking that this film had a
> composer to think of it's own ORIGINAL music?