title: drupal form alter
body: <p>I'm developing a module which alter display of add/edit node forms. I'm a beginner in module development.</p>
  
  <p>I have written following code, it is not working properly. Please tell me what's wrong with this?</p>
  
  <pre><code>function hook_form_alter(&amp;$form, $form_state, $form_id) {
    if ($form_id == 'node_form') {    
      drupal_set_message(t('some message.'));
    }  
  }
  </code></pre>
  
  <p>This is for drupal 6.</p>