Why do it yourself when we've already done all the work for you?
If you already have a DNS solution in place with the primary and secondary servers in the same location or network, consider our Secondary DNS Service.
Next job is to run DNSCMD /info in a command prompt.
Use our Dynamic Hostname service and get a name on one of our domains (ex: you.dtdns.net).
While you are on this tab, its worth setting the conflict resolution attempts to 3 or 4 which gives DHCP the opportunity to resolve any issues itself.
Once you have these credentials set, restart your DHCP server service.
Most of you won’t be running Windows 2003 anymore, but if you are, this link may be of interest: DHCP setup primarily is the place to start with this, it is often overlooked that there needs to be a username entered into DHCP to allow for these Dynamic Updates to take place.
This user account only needs limited privileges, it must be a member of DNSAdmins, DNSUpdate Proxy, DHCP Users and DHCP Administrators.