If the cards are identical, both should be detected when the module for the first is loaded. Try:
This will list the hardware information on all available network interfaces. If there isn't a listing for an eth1, then something might be a little off... Netgear is know to change a chipset slightly and not at all change the model information or packaging. Linksys is infamous for this. I doubt though that you're having this problem, RH's Kudzu has gotten a lot better in the past few years... but I don't think it automagically probes for a second card.
If it is there, first try bringing up the interface and getting it to do something before trying to automate it. For instance:
ifconfig eth1 192.168.0.4 up
and then ping something on that network. Adjust the IP for whichever network you're trying to build.
Offhand, is this going to be a NAT box? Just curious as that's the usual reason for a 2nd card.