navigation links ?!

already i have:

<?php query_posts('cat=3&showposts=10'); while (have_posts()) : the_post(); ?>
<?php the_title(); ?>
<?php the_excerpt ?>
<?php endwhile; ?>
<?php posts_nav_link(' - ','? previous','next ?') ?>

unfortunately it doesn’t work.
when i click on the next page it shows the same 10 recent posts as in the previous page.
bad loop?
help, please!