Before installing the new NIC into your system, enter the following commands:
#lspci -v
and
#ifconfig -a | more
Note from the output of these commands which NIC's base addresses are already in use on your system and write them down (assuming it is a PCI NIC). You can also enter the command:
#lsmod
This will display the currently loaded modules your kernel is using (if you are using a modular kernel). On a standard Red Hat installation (which uses a modular kernel), this command will show you the network driver module the system has loaded to support your existing NIC(s).