Dual NIC problems

I am trying to install a second Intel pro 100+ LAN card into my Windows NT4 server so that I can lighten the load on the existing card but the event manager reports a problem of confliction and then my server is unavailable to all users.

This question may be on about 5 million websites with solutions and may be easy to resolve but I am obviously not correct in my thinking.

Please help????

A very tired individual from UK.