I found and copied this post.I realize many people are way past this proplem,but maybe it will help someone.The following is what I found on www.linuxquestions.org
I think pretty much everyone with an NForce2 has this problem
Download and install nVidia's unified driver http://www.nvidia.com/object/linux_nforce_1.0-0261
(get the source tarball, not the rpm) and do the following steps:
1) tar xvfz nforce.tar.gz
2) cd /nforce/nvnet/
3) make && make install
Load up a text editor and open "/etc/modules.conf". Even if the file is empty, add the following line without the quotations: "alias eth0 nvnet" (not sure if this does anything, but you can also add the line "options nvnet optimization = 1")
7) modprobe nvnet
After this you should be set. If you don't have the nVidia unified driver installed, go ahead and do that too (from either the source you have downloaded or the rpm if you feel better about it).
I think I read further in the post it was important to get the .rpm and right click and install it first even though it appeared to do nothing when I did this.Then move on to the .tar file directions.For me the modprobe nvnet failed to locate the nvnet module.But upon reboot it did detect my onboard LAN.Hope this helps somebody.