It can be done, but I think it go'to deep for a dutch forum.
I can't answer you question for sure
see the manpage interfaces(5), specifically the up command.
put the route command in /etc/network/interfaces. There is a command that
executes arbitrary
commands when ifup (or ifdown) is called. See following example from one of
my machines.
iface eth0 inet static
address 67.66.8.41
netmask 255.255.255.248
network 67.66.8.120
broadcast 67.66.8.127
up /sbin/route add -host 67.66.8.41 eth0
gateway 67.66.8.46
You need to setup both nic's seperated...
Note:
Make the settings for eth0 match the network settings of the gateway machine. Set the gateway for the gateway machines ip.
Then give eth1 its own subnet, like 192.168.5.1, or whatever the existing network (with the clients) is using.
If the gateway resides on the internal network (and you won't be connecting them directly) then simply set eth0 with settings matching the internal network, and of course set the gateway.
You only need two nics if you are running two networks (LAN and one to connect to cable modem or ppp0 for dial-up modem).