5 posts per page from single category, paginated

Are you writing a custom query? If so, are you using the paged function in your query?

It would look something like this:

<?php 
    query_posts( array(
        'posts_per_page' => 5,
        'cat'            => '10',
        'paged'         => ( get_query_var( 'paged' ) ? get_query_var( 'paged' ) : 1 ),
    ) );

    while( $new_query->have_posts() ) : $new_query->the_post();
?>

  // loop stuff here

<?php endwhile; ?>

<?php next_posts_link( '&laquo; Older Entries', $new_query->max_num_pages ) ?>
<?php previous_posts_link( 'Newer Entries &raquo;' ) ?>