I want to use the autocomplete widget on a theme's search form. However I have no coding skills whatsoever , so any help is appreciated.

I've read on #727458: autocomplete for search form block that adding '#autocomplete_path' => 'apachesolr_autocomplete', will do the trick, however I'm not sure where can this be placed.
In my theme's folder, I got a search-theme-form.tpl.php with the following code :

<div id="search" class="container-inline">
    <?php $search['search_theme_form'] = '<div class="form-item" id="edit-search-theme-form-1-wrapper"><input type="text" maxlength="128" name="search_theme_form" id="edit-search-theme-form-1" size="15" title="" value="' . t('Enter keywords') . '" onfocus="if(this.value==\'' . t('Enter keywords') . '\'){this.value=\'\';}" onblur="if(this.value==\'\'){this.value=\'' . t('Enter keywords') . '\';}" class="form-text" /></div>'; 
 print $search['search_theme_form'];
	

print $search['submit'] = '<input type="image" name="op" id="edit-submit" class="form-submit" src="' . base_path() . path_to_theme() . '/images/theme-search-submit.png" title="Search" />';
print $search['hidden'];

?>

I also noticed that my template.php has a disabled section regarding altering search form :

/*function phptemplate_search_block_form($form) {
  //$form['search_block_form_keys']['#value'] = t('enter keywords');
  $form['submit']['#attributes']['title'] = t('Search');
  $form['submit']['#value'] = null;
  
  $output = drupal_render($form);
  $output = str_replace('class="form-item"','', $output);
  $output = str_replace('form-text','text', $output);
  $output = str_replace('form-submit','search', $output);
  $output = str_replace('</div>','', $output);
  $output = str_replace('div','p', $output);

  $output .= '</p>';
  return $output;
}*/

Do I have to enable the function phptemplate_search_block_form in template.php to use the autocomplete widget ? If so, in which file I must add '#autocomplete_path' => 'apachesolr_autocomplete', to use the autocomplete feature?

Anyone's help is appreciated!