Just to update this ancient thread for anyone interested, I was using my NAS to do this, but royally messed up by switching the NAS off while on holiday, forgetting the CCTV remote viewing relied on the DynDNS updates it was doing.
So, I've been playing with the DynDNS update in the cameras with little joy, gave up and decided to look at the Home Hub again, and spotted my mistake - I had used my email address (which you can use to sign in at dyndns.com) and not the username!
So, to set up DynDNS go to http://192.168.1.254/bb_ddns.lp?be=1&l0=2&l1=2&l2=3
Use Dynamic DNS service - Yes
Username - Your *user name* for DynDNS - not the email!
Password - Password as used to log into DynDNS
Service - dyndns (though it claims to do several others I've no need to try)
Use multiple hosts - No (in my case, I only use one)
Host - the host name exactly as in your DynDNS account. No http:// prefix.
Once you have saved this, go to the Event log, http://192.168.1.254/log.lp?be=0&l0=3&l1=3&l2=-1
and if all is well you should see the following lines,
23:51:08 5 Oct DYNDNS Host *your DynDNS domain's name* has been updated successfully by members.dyndns.org
23:51:08 5 Oct DYNDNS client dyndns_0 started
23:51:07 5 Oct DYNDNS client dyndns_0 stopped
If it hasn't worked, you may see an error like this,
01:00:59 1 Jan DYNDNS Connection failed to members.dyndns.org for client dyndns_0
in which case go back and check through the username, password and host.
As a final double-check, go to your DynDNS account and check when the IP address was last updated. Due to different time zones the hour may not match, but the minutes will.