ipcop and network settings

[dbclinton]

Hi,
I've put a PC running the Ipcop firewall between the Internet and my
Edubuntu thin client server (Intrepid). The network card that connects
Ipcop to my server (green) has these settings:
=================
eth0      Link encap:Ethernet  HWaddr 00:08:A1:1E:73:90  
          inet addr:192.168.1.1  Bcast:192.168.1.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:2062 errors:227 dropped:0 overruns:0 frame:0
          TX packets:2215 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:369386 (360.7 KB)  TX bytes:1424440 (1.3 MB)
          Interrupt:12 Base address:0xe800 
=================
To get my server to play nicely with Ipcop, I had to disable
my /etc/network/interfaces file - which looked like this:
=================
auto eth1
iface eth1 inet static
	address 192.168.0.254
	netmask 255.255.255.0
	network 192.168.0.0
	broadcast 192.168.0.255
	gateway 192.168.0.1
	# dns-* options are implemented by the resolvconf package, if installed
	dns-nameservers 192.168.0.1
	dns-search clinton

auto eth0
iface eth0 inet static
    address 192.168.0.254
    netmask 255.255.255.0
    network 192.168.0.0
    broadcast 192.168.0.255 
===================

...which got me talking nicely to Ipcop but which also, of course,
brought my thin clients to a screaming halt.
So I assume I have to reconfigure my server settings. My first question
is: which ip settings can I safely use?
Next, besides /etc/network/interfaces and /etc/ltsp/dhcpd.conf, are
there any other files I'll have to know about?
With thanks as always,
David Clinton