ok, put in an ethernet card that has been detected, then open a terminal or console as root
then type "ifconfig", that should show the card if its active, if not type "dmesg | more" and scroll thru that and see if its detected at boot up, if it is then type:
ifconfig eth0 <netaddressyouwant> up and see what happens, example ifconfig eth0 192.168.0.1 up
then type ifconfig again and it should show it running and working
sometimes the gui setup apps like netsetup in redhat dont freakin work right or are misleading to newbies
for complete explanation of ifconfig type "man ifconfig" in a terminal