How to add the value of a drupal field to the class of a wrapper div
Something like this should do it:

function MYTHEME_preprocess_node(&amp;$vars) {
  if ($vars['node'] == 'some_type') {
    $field_items = field_get_items('node', $vars['node'], 'field_name');
    $first_item = array_shift($field_items);

    $value = $first_item['value'];

    // If you want to write &lt;div class="&lt;?php echo $extra_class; ?&gt;"&gt;... in your template file:
    $vars['extra_class'] = $value;

    // Or if you want to add this to the classes on the main node &lt;div&gt;:
    $vars['classes_array'][] = $value;
  }
}