Hi

Personally I don't use RedHat but anyway this is what i would check/try .

What kind of network card you got ?
I suppose you use the standard redhat kernel. Check if the kernel supports your card.

If it does, try to figure out which module supports the card.

Then test the card like this :

modprobe modulename
(e.g. eepro100 for a Intel EtherExpress,
3c90x for a 3Com 905C-TX etc.)

ifconfig eth0 192.168.1.1 up

Obviously replace the IP with the one you want for the system. After that try to ping another machine on the network.
If that works make the changes permanent.

If it still does not work, type dmesg and check its output. You may find some issues there.

Hope that helps.