I don't think this discussion gets to the point.

While I usualy run a caching name server behind a NAT router, I don't think
it should be necessary. It is not much risk in this situation, if you do
not run it on the NAT router itself or have it listen to the external
address (why should you want that?)

Anyway, it is not *needed* to make the network behind the NAT work. There is
another configuration error, or the original problem would not have shown
up.

How does the Mac get it's IP address and settings? Is it hardwired? Or do
you run dhcpd? In the latter case, add 

 option domain-name-servers X.X.X.X;

to your /etc/dhcpd.conf file. In the former case, there needs to be a way
to explicitly tell it the DNS address (like /etc/resolv.conf in NetBSD).

You can point the Mac to the external name server (typically of your ISP) and
it should be able to query that just fine. If not, there is an error that
you should fix, not hide by running a local server.


Martin