Where is King Kong? I saw him on the official poster.
He was not in the film. He was put on the poster for "advertising".
What are the differences between the r-rated and unrated version?
The film was released in both the theatrical and the unrated version on DVD. The theatrical cut has been rated PG-13 by the MPAA (for crude and sexual humor throughout, some comic violence and language), the unrated version basically contains all the material that would have been too much for the rating. The unrated version runs 357 seconds = 5 minutes 57 seconds (PAL) longer than the PG-13-Rated theatrical version. A detailed comparison between both versions can be found here.
What is the significance of the president reading a book about ducks with school children?
Leslie Nielsen (president Harris) is told the nation is under attack by aliens by his advisor while reading with school children. Nielsen wants to continue reading. This is spoofing George Bush who was reading with school children on September 11th 2001. When told of the attacks by his advisor, Bush kept reading instead of acting.