Hi
The IPcop will support a third nic, red,green,orange.
Depending on what you are trying to do, you may want to place the sme on the orange nic.
The orange nic is where you want your sme server, orange doesn't have nating firewall and you would be able to access orange from green but orange can't access green by default. You still would forward ports from green to orange and pinhole from orange to green if needed. Having the sme on green presents itself with many problems, one being you end up exposing green(lan)and that defeats the purpose of the firewall on green.
If your intent is to have a web server on the sme then it is recommended to put the sme on orange and not on green.
As you may know IPcop is a fork of Smoothwall and I do have a smoothie w/3 nics and it works fine w/sme on orange in server/gateway mode. I would imagine you might have many problems setting up sme on green in server/gateway mode, havn't done that and won't do it due to the security issues imposed on green (lan)for one.
One of these days I'm going to try the cop.
More specific info as to what your trying to do would help.
Later