Try something like this…..
<?php query_posts(cat=12&posts_per_page=10&paged=' .$paged); ?>
<?php while (have_posts()) : the_post(); ?>
<div <?php post_class() ?> id="post-<?php the_ID(); ?>">
<h2><?php the_title(); ?></h2>
<div class="post-info">
<b><?php the_time('l, d F Y H:i'); ?></b>
<div class="post-block">
<?php the_content(); ?>
</div>
</div>
</div>
<?php endwhile;?>
<?php wp_pagenavi(); ">
the query_posts function accepts several arguments…one of which is posts_per_page. I threw in the cat=12 as an example of specifying a category. Try going with the posts_per_page rather than showposts and see if that works. I do something similar on my own site.