I ran into the same problem (no lan) with my Shuttle SN41G2 with Redhat 9. I tried installing the .rpms for the problem but they wouldn't show up when i tried to do a modprobe nvnet.
Then I downloaded the .tar.gz version of the nforce drivers, and got them to work. After you un-tar the drivers, you'll find there's a nforce/nvnet directory under your current directory. I did the following that works:
and then made sure that my "alias eth0 nvnet" line was in /etc/modules.conf file.
This worked quite well with the 2.4.20-8 kernel that comes on the RedHat 9 base install, but when i upgraded to 2.4.20-9 it wouldn't work, so I am booting from 2.4.20-8 from the grub boot-loader screen until I can find the new driver from NVIDIA that supports Redhat 9.