How should I configure my two lancards on my Debian system?

[Sonixxfx]

Hi,

I have a linux box connected directly to the internet that has two lan cards installed on it. I would like to connect two other computers to those cards so that they can make use of the internet connection. Can someone tell me how I should configure those cards to achive this?
I actually already have a setup that makes it possible for one pc to connect to the internet using one of those cards, but I do not no how to configure the other. I have been thinking about a different subnet and bridging but I didn't really came further than that.

Thanks for your help,

Ben