im currently adding new custom fields to users in prestashop 1.5.xx in the front view is easy....
only change the authentification.tpl in your theme folder and add this line:
<p class="text">
<label for="custom_1">{l s='custom_1'}</label>
<input type="text" class="text" name="custom_1" id="custom_1" value="" />
</p>
and next add this line in customer.php controller, in public static $definition = array( :
'custom_1' => array('type' => self::TYPE_STRING, 'validate' => 'isGenericName'),
the last step is add custom_1 field in ps_customer table in MYSQL
the only task that need is show fields in administration.....
Bye