function addUser($username, $password, $additional = "")
    {
        if (function_exists($this->options['cryptType'])) {
            $cryptFunction = $this->options['cryptType'];
        } else {
            $cryptFunction = 'md5';
        }

        $additional_key   = '';
        $additional_value = '';

        if (is_array($additional)) {
            foreach ($additional as $key => $value) {
                $additional_key .= ', ' . $key;
                $additional_value .= ", '" . $value . "'";
            }
        }

        $query = sprintf("INSERT INTO %s (%s, %s%s) VALUES ('%s', '%s'%s)",
                         $this->options['table'],
                         $this->options['usernamecol'],
                         $this->options['passwordcol'],
                         $additional_key,
                         $username,
                         $cryptFunction($password),
                         $additional_value
                         );

        $res = $this->query($query);

        if (DB::isError($res)) {
           return PEAR::raiseError($res->getMessage(), $res->getCode());
        } else {
          return true;
        }
    }