<?php
add_filter( 'the_password_form', 'custom_password_form' );
function custom_password_form() {
    global $post;
    $label = 'pwbox-'.( empty( $post->ID ) ? rand() : $post->ID );
    $o = '<form class="protected-post-form" action="' . get_option('siteurl') . '/wp-pass.php" method="post">
    ' . __( "This post is password protected.  More than likely it is password protected because it is a free gift for people who subscribe to my newsletter.  <a href=\"#newslettersubscribe\">newsletter</a>") . '
    <label for="' . $label . '">' . __( "Password:" ) . ' </label><input name="post_password" id="' . $label . '" type="password" size="20" /><input type="submit" name="Submit" value="' . esc_attr__( "Submit" ) . '" />
    </form>
    ';
    return $o;
}
?>