Drupal 6.x Block Example

drupal-6-hook_block.php

<?php 

function all_projects_block($op = 'list', $delta = 'all_projects_link') { // Make the delta a string, it is easier!
  $block = array();
  switch ($op) {
    case 'list':// This lists the block in the admin>blocks page
      $block['all_projects_link'] = array( //You have to reference the delta for $op 'list' otherwise it won't work
      'info' => t('2.1-All Projects Block'),
      'weight' => 0,
      'status' => TRUE,
      'visibility' => '1',
      'pages' => '<front>',
      'region' => 'header',// The region should exist in your theme!
      );
      return $block;
    case 'view'://This displays the block on the page.   
       $block = array( //You can't reference the delta here during $op 'view'
       'subject' => t('All Projects'),
       'content' => '<em>Bawk!</em>',

       );
      }
      return $block;
}

?>
// There is a variable set in the block table that is the same as the $delta in the database that you should delete when testing block code.