The missing link is the file that receives the information and inputs into the database.
Think that line 121 of register.php is where you will need to amend:
Code:
db_query("update $sql_tbl[customers] set password='$crypted', password_hint='$password_hint', password_hint_answer='$password_hint_answer', title='$title', firstname='$firstname', lastname='$lastname', company='$company', b_address='$b_address', b_city='$b_city', b_state='$b_state', b_country='$b_country', b_zipcode='$b_zipcode', s_address='$s_address', s_city='$s_city', s_state='$s_state', s_country='$s_country', s_zipcode='$s_zipcode', phone='$phone', email='$email', fax='$fax', url='$url', card_name='$card_name', card_type='$card_type', card_number='".text_crypt($card_number)."', card_expire='$card_expire', card_cvv2='$card_cvv2', pending_membership='$pending_membership', ssn='$ssn' where login='$login' and usertype='$login_type'");
make sure that your new fields are added into this sql query.
ie:
, newfield1='$newfield1', newfield2='$newfield2'
where the $newfield1 is the name of the form input field and newfield1 is the name of the db field.
hth