from command line while logged in as root:
dmesg | more ---------that will show the boot up message,check it to see if your network card was recognized by the kernel
lspci --------will list all pci devices on your system
lsmod ---------will list all kernel modules loaded, check if NIC has its kernel module in that list
insmod <module_name> will load the appropriate module if it isnt loaded, then change the appropriate init script so it gets done at boot, Redhat uses systemV init scripts
ifconfig -------use this to set IP address,netmask, and other settings for the NIC(s) in your system
if your sharing a connection with a windows machine using it as a router, you will have to setup the NIC in the linux box to use DHCP as well