[exim] LAN relaying

Background:
-------------
I've managed to set up exim to use (be?) a smart host, and upstream to
my ISP etc, but I can only send mail from my mail server.

Short Question
--------------
Any other computers on the local lan are able to establish a session
with the server, but eventually get a "relay not permitted" error.
What's my one line fix that will make this problems go away?

Additional Info
---------------
I've tried changing update-exim4.conf.conf with
dc_local_interfaces='192.168.1.1,192.168.2.1', and
dc_relay_domains='192.168.0.0/16'

Network topology is wireless (with dsl router) on 192.168.2.* and wired
on 192.168.1.*. (server has 2 network interfaces)

Linux: Debian stable
Exim4

Manual Reference
-----------------
(Oops! I've been using the 4.1 manual instead of the latest - much
nicer!) Section 39.39:

In the main part of the configuration, you put the following definitions:

domainlist local_domains = my.dom1.example : my.dom2.example
domainlist relay_domains = friend1.example : friend2.example
hostlist relay_hosts = 192.168.45.0/24

I'm pretty sure the last line relates to me - but how do I do this in
debian? something in update-exim.conf.conf?

Other Ramblings (Are my thoughts mainly correct?)
----------------------------------------------------
As additional (non problem) info, it seems that there are a few
different exim conventions across the linuxes, which is confusing. I'm
working through the manual to try and grok the system properly. I
figure I just need to find out how to configure the ACL's for entire
subnets.

Also, I'm a bit nervous about running the debconf thing again as I feel
it might destroy some things that I've gotton right this time round....
should I be afraid?


Thanks heaps
Stephen