Get the content of a specific page (by ID)

<?php

// would echo post 7's content up until the <!--more--> tag
$post_7 = get_post(7); 
$excerpt = $post_7->post_excerpt;
echo $excerpt;

// would get post 12's entire content after which you
// can manipulate it with your own trimming preferences
$post_12 = get_post(12); 
$trim_me = $post_12->post_content;
my_trim_function( $trim_me );

?>