render html no formatting

You have to implement your own hook for template_redirect action:

add_action( 'template_redirect', 'wpse8170_template_redirect', 1 );
function wpse8170_template_redirect() {
    global $wp_query;

    // check if it is not a page or if it is front page, then exit from the hook
    if ( !$wp_query->is_page() || $wp_query->is_front_page() ) {
        return;
    }

    // check queried object, if it is not a specific page, then exit from the hook
    $page = get_queried_object();
    if ( $page->ID != 777 ) { // your page ID 
        return;
    }

    // render header
    get_header();

    // ... render your content here ....

    // render footer
    get_footer();

    exit;
}