is there a version of BIND that supports dynamic updating?
i'm pretty sure the answer's no, but i just thought i'd verify...
On master, set allow-update { client.ip.addr.here; };
On client, run nsupdate.
unless the client ip is truely dynamic (such as a dialup with a large modem pool) then you may have to resort to using dnssec-keygen to create a key hash for the client /server to use to authenticate the update request.
See the bind home page FAQ for more info as it's rather involved. Also see the man pages for dnssec-keygen, nsupdate, (rndc.conf | named.conf)