My network interface worked great before installing the NVidia video drivers, but after it's dead. The eth0 interface is still there, it has an IP address (which I think is from the last reboot) but I can't ping anything including the router, resolve domain names or make any TCP connections.

I'm running KUbuntu 8.04, but the same thing happened on Ubuntu 8.04. The motherboard is an Asus A8V-VM SE which uses the RTL8201CL ethernet chip. I tried to diagnose the problem, but as far as I can see everything is how it should be.