Show only one post for day and comments in sidebar

Escuse, i need show post for certain categories in sidebar with the comments on it, or, for extern news I will have the opportunity to add comments in the news.
It’s possible?

Hello how i can show one post for selected category in sidebar??

One example (doesn’t address your comments):

<?php
//get 5 recent posts in categories 3 or 19.  Useful for sidebar or php code widget
    $args=array(
      'showposts'=>5,
      'category__in' => array(3,19),
      'caller_get_posts'=>1
    );
    $my_query = new WP_Query($args);
    if( $my_query->have_posts() ) {
      echo '5 recent Posts';
      while ($my_query->have_posts()) : $my_query->the_post(); ?>
        <p><a href="<?php the_permalink() ?>" rel="bookmark" title="Permanent Link to <?php the_title_attribute(); ?>"><?php the_title(); ?></a></p>
       <?php
       the_content();
      endwhile;
    } //if ($my_query)
  wp_reset_query();  // Restore global post data stomped by the_post().
?>

Thanks it work good, but i need show limitated number of characters and if possible add comment number or “Add reply”, how i can do it?

1. Replace the_content(); with echo 'this is 40 chars of content >' . substr($post->post_content,0,40);
2. Template_Tags/comments_popup_link

Thanks a lot!!!

This is awesome, thanks!!