The taxonomy module uses the [taxonomy_term_page][2] function to build the page that list the nodes attached to a term. But the function that really do the query is the [taxonomy_select_nodes][3] that is called by this previous function.

So you can implement a custom module and use the [hook_menu_alter][1] to rewrite the `page callback` for the `taxonomy/term/%taxonomy_term` path using a new function based on the `taxonomy_term_page` to call your second custom function also based on the `taxonomy_select_nodes` that changes the query to order the nodes the way you need.

Notice that will change the behavior of all taxonomy term pages.

For more info about how to create a custom module see http://drupal.org/node/361112.


  [1]: http://api.drupal.org/api/drupal/modules!system!system.api.php/function/hook_menu_alter/7
  [2]: http://api.drupal.org/api/drupal/modules!taxonomy!taxonomy.pages.inc/function/taxonomy_term_page/7
  [3]: http://api.drupal.org/api/drupal/modules!taxonomy!taxonomy.module/function/taxonomy_select_nodes/7