Customising admin controller.php

I have customised my AdminUsersController.php to show custom fields in particular order.

Only problem im having is the custom field checkboxes. My code is;

Code:

$nameField->addElement('text', 'name_f', array('size'=>20));
$nameField->addElement('text', 'name_l', array('size'=>20));
 
 
$fieldSet->addElement('advcheckbox', 'additionalcopies', array('id' => 'additionalcopies', ))
            ->loadOptions(array(
                '1'  => 'One',
                '2'  => 'Two',
                '3'  => 'Three',
            ))->setLabel(___('>Additional Copies Required'));

How can I correct my code to read the user checkbox they selected on signup?

Regards.
Zack