UNIFIED_NODE_EDIT_PAGE-template.php

<?php
/**
 * Unified node edit/add page template suggestion for Drupal 6.x
 *   Filename: page-node-edit.tpl.php
 *   Rearrange the $vars['template_files'] array, put
 *   'page-node-edit.tpl.php' to the end of array.
 * 
 *   (use this snipet in template.php, at the and of 
 *    'MYTHEME_preprocess_page' function)
 */

function MYTHEME_preprocess_page(&$vars) {
  if (arg(0) == 'node' && (arg(1) == 'add' || arg(2) == 'edit')) {
    $edit_page_tpl_key = array_search('page-node-edit', $vars['template_files']);
    if ($edit_page_tpl_key !== FALSE) {
      unset($vars['template_files'][$edit_page_tpl_key]);
    }
    $vars['template_files'][] = 'page-node-edit';
  }
}
?>