no network access on 2nd nic

Have 2 nic's, 1 for internet and 1 for intranet. Internet works fine until I set up #2 with default gateway then I get a error message when leaving properties box. something about redundant default gateways. If I leave this in place #1 network stops working. I have tried to just setting #2 to auto both ip and gateway. I can't even ping the server. It doesn't leave the computer. I thought it was the nic card because i riped it out of the old computer and the driver wouldn't work for the W7. So I bought a new one that was compatible with W7. Nothing has worked. The problem is that this is not my computer it's my wifes, and she's not a happy camper. This set-up worked on the XP that was taken out of service and replaced with the Windows 7.