I’ve added my how-to on setting up dynamic DNS with Bind and DHCP to the wiki.  It’s based on CentOS 5.3 but should easily be applied to any Linux/Unix/BSD.  You can find the how-to at http://www.rainingpackets.com/wiki/doku.php?id=dynamic_dns_with_bind_and_dhcp_on_centos.  If you have comments or corrections, drop me a line.