You aren't making any sense. Are you running a web server that you only want accessible from your box? If so, just run it on localhost. Do you have more than one box, and you want all of them to be able to access the webserver on that box, but not other people on the internet? Set up your network and webserver to answer on only one of the ethernet cards and put a rule in your iptables to only allow access from your internal machines, dropping all others.
I'm not sure where to point you. You are using some of the correct terms, but networking doesn't work the way you are trying to make it. Each ethernet card must answer a different subnet or your machine won't know how to route packets, and will therefore not know how to get answers back from other machines.
I guess if you started over and let us know what you wanted as an outcome without trying to guess as to how to do it, the question would be easier to answer.