How to display posts first from one category and then from other on tag.php temp

Below code will work fine for you.

<?php
query_posts($query_string . '&cat=1'); // Services
  if ( have_posts() ) : while ( have_posts() ) : the_post();
    /* do stuff */
  endwhile; endif;
wp_reset_query();

query_posts($query_string . '&cat=2'); // Publications
  if ( have_posts() ) : while ( have_posts() ) : the_post();
    /* do stuff */
  endwhile; endif;
wp_reset_query();
?>

For example,
1 as category ID for “Services” and 2 as category ID for “Publications”.