As I said, I don't know if any of this will work for you, as I use "ISC" bind, and you are using some IPlanet product.
All configuration files are plain text, editable by "vi". ISC DNS server, named, is configured through a plain text file called named.conf. Inside this file there is typically a statement that tells where all "included" files are kept (in this case, zone files).
Under Sun and HP/UX default named scenarios this is not set, and all dependant files are assumed to be in /etc/.
[ Under Linux zone files are kept in /var/named. ]
You will not have a blank zone file at all, until you create one. vi /etc/blank.zone. Then simply add all of the lines that I put in my previous example (which had settings, but no entries). Then for each zone you are trying to block, you would add that zone to the named.conf file.
It sounds like you should really seek some assistance with IPlanet specifically though, as I doubt my advice will go far with your setup - and while IPlanet is affiliated with Sun, it is not standard on Sun systems.
Thanks,
Allen