Well I guess one of the questions is if RedHat has even detected your NIC. One place to look would be to 'cat' your /proc/pci file and see if there is a reference to your ethernet card. If there is, then it is likely that the OS thinks it has found your card and is running it. If not you may have to do some digging to find out what type of ethernet card is in your box and see if someone has been kind enough to work out a procedure for getting it recognized.
Assuming that the OS is seeing the card, then it might be worthwhile to run 'ethtool' to see if it thinks that it has an establish link. If not you might want to investigate your cable, your speed and duplex settings, etc... If you do have a link established, but you still do not have an IP address, check to make sure that you are set up for DHCP (if that is your intention), make sure that you have something available to provide an IP address for the DHCP request.
If you have gotten this far and all is well, but you cannot seem to get a dynamic address you may want to try to set a static IP address within your network range and see if you can communicate.