Answer by andrewsi for Wordpress: Unlimitet Posts on specific Page

You can over-ride the settings from the admin page programmatically. You're going to need to tweak your query, though, and over-ride the loop. I think something like this will work:

global $wp_query;

$args = array_merge( $wp_query->query_vars, array( 'posts_per_page' => '-1' ) );
query_posts( $args );

while ( have_posts() ) : the_post();
    the_content();
endwhile;

(I'm putting this together from a couple of different man pages, so it might not be perfect; but it should point you in the right direction)

Effectively, you're making a new query for posts (the query_posts call). You're passing it a new set of parameters, created from the existing ones via the array_merge; and you're explicitly setting posts_per_page to -1, which should turn off the limit for the number of posts.