Hi, The Asus motherboard of recent times seem to all be using the Broadcom BCM4400 series ethernet controllers. Redhat's support for this has been spotty. I don't remember if it was supported on RH9. Luckily it wasn't that difficult for me to fix on my A7V333-X machine:
1) Double check that it is the bcm4400 family using lspci as root.
2) If it is, then on your Asus CDROM they supplied a drivers directory that has the driver source code. Place it in a directory somewhere and build it. (As user type 'make'. If everything goes OK, then as root type 'make install'.)
3) You can load it by hand just typing 'modprobe bcm4400' or you can alias it in your modules.conf file.