Please don't push threads. Ppl going through unreads posts / threads will answer in case they know something.
I don't much in this case because I do not use the NS function of ISPConfig as most NICs require to have at least two Nameservers responsible for a zone (so I do not want to setup a second server as slave of my ispconfig machine) and besides this my domain registrar servers me with nameserver service for free.
Anyway, you have to set you ISPConfig machine as authoritative for your domains with your domain registrar, which nameservers to use. From my point of view that's it.
Regarding the dyndnsthing, you may take a look at nsupdate (http://linux.yyz.us/nsupdate/
) but I don't know if it will get in conflict with ispconfig when regenerating the zonefiles.