how do I get a single DNS to return addresses based on query source address

[Yossie Silverman]

The problem:

I would like to have a single DNS server (bind) running on my 
network.  This server should return an internal (non global) address 
when the source address of the query is internal as well.  Otherwise, 
it should return the external (global) address.  From what I can tell 
from the docs, sortlist (in options) SHOULD be able to do this, but 
it isn't clear exactly how to get it to do so.

E.g.

Internal network: 192.168.1.0/24

If a query comes from this network, for 'mail', the resolved address 
should be 192.168.1.5.  If it comes from outside this network, the 
resolved address should be 216.135.198.111 (all addresses are 
"fictitious").

Thanks! - Yossie