php4 code not working under php5

hi,
i use this php dns resolver class ( http://www.ypass.net/software/php/Net_DNS/ ), and it works under php4. however, i have to move this whole project to a php5 server. now the shit hits the fan because the guy who wrote this class back in 2002 tries to reassign $this ($this = $this->...):

    function Net_DNS_RR($rrdata)
    {
        if (is_string($rrdata)) {
            $this = $this->new_from_string($rrdata);
        } else if (count($rrdata) == 7) {
            list ($name, $rrtype, $rrclass, $ttl, $rdlength, $data, $offset) = $rrdata;
            $this = $this->new_from_data($name, $rrtype, $rrclass, $ttl, $rdlength, $data, $offset);
        } else {
            $this = $this->new_from_array($rrdata);
        }
    }

PHP:

does anyone know how to fix that, without rewriting everything...?