Form not showing in administration menu in Drupal6
You have an an underscore (_) in page_callback. Remove that, clear the caches, and you should be good to go.

function ptm_autocomplete_menu() {                                              
  $items['admin/prestum/autocomplete'] = array(                                 
    'title' =&gt; 'Autocomplete',                                                  
    'description' =&gt; 'Autocomplete',                                            
    'page callback' =&gt; 'drupal_get_form',                                       
    'page arguments' =&gt; array('ptm_autocomplete_form', array(), array()),       
    'access arguments' =&gt; array('access administration pages'),                 
  );                                                                            

  return $items;                                                                
} 


Also if this is Drupal 7 your form function should have $form as the first param:

function ptm_autocomplete_form($form, &amp;$form_state, $unused, $form_values) { ...


But not for Drupal 6.