Don't know of any sites but to get the NVidia Network card working, you need to compile the nvnet module for your kernel.
Chances are you just need to download the RPM for your system from:
There are two prebuilt RPMs for RH9, for kernel 2.4.20-6 and 2.4.20-9. If that doesn't match your running kernel (type "uname -r" at a command prompt) you'll need to compile the module yourself.
If that does match, download the RPM and install it (type as root "rpm -Uvh file.rpm"). You may have to add the line "alias eth1 nvnet" to your /etc/modules.conf file.
If you have to build your own: make sure you have the kernel-source RPM installed (should come with Redhat) and download the src.rpm file from the above link. Then type as root "rpm --rebuild file.src.rpm" This should rebuild the necessary modules for you and give you an rpm file in /usr/src/RPM/RPMS/athlon/ (the last folder name could be i586 or something). You can then install this RPM as above.
Hope this helps.
PS Oh, this is for a Mandrake system, but the same should be true of Redhat, although it's been a while since I fiddled with Redhat.