Adding CSS and JS to form with attachments
Have you looked at the documentation?

Attach CSS and JS to form

http://api.drupal.org/api/drupal/developer!topics!forms_api_reference.html/7#attached

$form['#attached']['css'][] = drupal_get_path('module', 'ajax_example') . '/ajax_example.css';

$form['#attached']['js'][] = drupal_get_path('module', 'ajax_example') . '/ajax_example.js';


External files

http://api.drupal.org/api/drupal/includes%21common.inc/function/drupal_process_attached/7

External 'js' and 'css' files can also be loaded. For example:

$build['#attached']['js']['http://code.jquery.com/jquery-1.4.2.min.js'] = array('type' =&gt; 'external');