Theme search form in drupal 7

There is no search box any more in D7. Use _preprocess_search_block_form instead. See http://drupal.org/node/254940#search_box

hi koen try this code ... for me it works :)

function hook_mi_form_alter(&$form, &$form_state, $form_id) {  
   
 if ($form_id == 'search_form') {
   
$prompt = t('Enter your keywords'); /* change this $prompt */
$keys = t('search...'); /* and this one */

  $form['basic'] = array(
    '#type' => 'container',
    '#attributes' => array('class' => array('container-inline')),
  );
  $form['basic']['keys'] = array(
    '#type' => 'textfield', 
    '#title' => $prompt, 
    '#default_value' => $keys, 
    '#size' => $prompt ? 40 : 20, 
    '#maxlength' => 255,
  );

  $form['basic']['processed_keys'] = array(
    '#type' => 'value',
    '#value' => array(),
  );
  $form['basic']['submit'] = array(
    '#type' => 'submit',
    '#value' => t('value for search button'), /* take a look here */
  );

	
   // Advanced search start here hwg!
    $form['advanced'] = array(
      '#type' => 'fieldset', 
      '#title' => t('advanced search'),  /* you can change this too */
      '#collapsible' => TRUE, 
      '#collapsed' => FALSE, 
      '#attributes' => array('class' => array('search-advanced')),
    );
    $form['advanced']['keywords'] = array(
      '#prefix' => '<div class="criterion">', 
      '#suffix' => '</div>',
    );
    $form['advanced']['keywords']['or'] = array(
      '#type' => 'textfield', 
      '#title' => t('OR'),  /* here too */
      '#size' => 30, 
      '#maxlength' => 255,
	  '#description' => t(''), /* u can add a little description too */
    );
    $form['advanced']['keywords']['phrase'] = array(
      '#type' => 'textfield', 
      '#title' => t('ur phrase'),  /* here :) */
      '#size' => 30, 
      '#maxlength' => 255,
	  '#description' => t(''),
    );
    $form['advanced']['keywords']['negative'] = array(
      '#type' => 'textfield', 
      '#title' => t('negative words :)'),  /* and here */ 
      '#size' => 30, 
      '#maxlength' => 255,
	  '#description' => t(''),
    );

    // Node types:
    $types = array_map('check_plain', node_type_get_names());
    $form['advanced']['type'] = array(
      '#type' => 'checkboxes', 
      '#title' => t('choose types'),  /* another title that u can change */
      '#prefix' => '<div class="criterion">', 
      '#suffix' => '</div>', 
      '#options' => $types,
    );
    $form['advanced']['submit'] = array(
      '#type' => 'submit', 
      '#value' => t('value for advanced search button'),  /* and the last one :) */
      '#prefix' => '<div class="action">', 
      '#suffix' => '</div>', 
      '#weight' => 100,
    );

    // Languages:
    $language_options = array();
    foreach (language_list('language') as $key => $entity) {
      if ($entity->enabled) {
        $language_options[$key] = $entity->name;
      }
    }
    if (count($language_options) > 1) {
      $form['advanced']['language'] = array(
        '#type' => 'checkboxes', 
        '#title' => t('Languages'), 
        '#prefix' => '<div class="criterion">', 
        '#suffix' => '</div>', 
        '#options' => $language_options,
		'#description' => t(''),
      );
    }

    $form['#validate'][] = 'node_search_validate';
  }
   
}