// En el phptemplate
 
 function phptemplate_radio($element) {
 
  // Create a random number to append to the ID
  //This is required as with e.g. poll mudule, the poll
  // node appears twice resulting in duplicate IDs
 
  $new_rand_no = (mt_rand(10,1000000));
 
  _form_set_class($element, array('form-radio'));
  $output = '<input type="radio" ';
  $output .= 'name="' . $element['#name'] .'" ';
  $output .= 'value="'. $element['#return_value'] .'" ';
  $output .= 'id="'. $element['#id'] . '_' . $element['#return_value'] . $new_rand_no .'" ';
  $output .= (check_plain($element['#value']) == $element['#return_value']) ? ' checked="checked" ' : ' ';
  $output .= drupal_attributes($element['#attributes']) .' />';
  if (!is_null($element['#title'])) {
    $output = '<label class="option" for="' . $element['#id'] . '_' . $element['#return_value'] . $new_rand_no .'">'. $output .' '. $element['#title'] .'</label>';
  }
 
  unset($element['#title']);
  return theme('form_element', $element, $output);
}
 
 
// En una función form_alter
if ($form_id == 'simplenews_block_form') {
    $form['mail']['#default_value'] = 'correo';
}