A little info might help. What type of network? 100Base-T? Both? What protocol(S)? What is your network layout? Do you have 400000 machines but only 4 should be able to access both networks? If not, why not combine them? What OS are you using? Generally speaking, you would have to add the second network card the the machine, bind it to your protocol, and set up routing. With TCP/IP, you can set this up by setting up a TCP/IP address and subnet mask. You will need to decide how you want to handle routing. If you put a default gateway in the config for both cards, your performance will tank. Again, depending on your network numbering scheme, you may be able to leave the mask open on one NIC or the other. Be careful when you set this up that your masks DO NOT overlap.