in-addr.arpa deligation

[Ruslan]

I have primary zone and one deligated zone(xxx.ru and hq.xxx.ru).For
primary db file is:
@    IN SOA xxx.ru .... ()
        IN NS    ns.xxx.ru.
        IN MX    ...
hq    IN NS    ns.hq.xxx.ru.  ; deligated zone
        IN MX    ...
ns.hq    IN A ..... ; glue record
and how can I deligate in-addr.arpa zone in order someone outside can
translate IP to name in 'hq' zone.