While using my iMac today I had a very strange network failure, which I attributed to Parallels Workstation at first.
Built-in Ethernet suddenly lost its IP address and would no longer connect. All attempts to obtain an IP address failed. In the network setup panel I noticed a new port, vi2, which is Parallels’ bridged network interface. The new interface had a valid IP address in the 10.x.x.x range, although my home network uses the 192.168.0.x range. The only way I could get network connectivity was with Airport. Unloading Parallel’s KEXT also didn’t fix it.
Finally I tried swapping among the ports on my Linksys ethernet switch and it suddenly started working. My G4 still worked when connected to the port my iMac was originally connected to, so it’s not a bad port.