<select size='6' name="id">
  <?php foreach($msgs as $msg):
     if(!isset($_SESSION['zalogowany']) && $msg['registered']){
       $disabledstr = 'disabled="disabled"';
       $id = '-1';
     }
     else{
       $disabledstr = '';
       $id = $msg['id'];
     }
  ?>
  <option value="<?php echo $id; ?>" 
    <?php echo $disabledstr; ?>><?php echo $msg['title']?></option>
  <?php
    endforeach;
  ?>
</select>
