zone definition help request

[carinus.carelse at mrc.ac.za]

I have several virtual domains that I am responsible for.  They are 
usually web addressess and as such have to be teid to a public address on 
the firewall.  We have an internal dns server I would like the dns server 
to not resolve the external address but the internal address so that the 
internal clients don't have to go through the firewall to get the page.  I 
have this working for one domain but the way I did it was to create a 
specific zone for the domain on the dns server I have about 20 domains and 
I would like to know if there is a way I can setup one zone to encompass 
all the various domains in one file or do I have to create a seperate zone 
file for each domain.
Please can someone assist me.

Carinus