How to tell if Ethernet Port is fried?

Need some help. My father in law had a power failure at the house, and since then, he cannot connect to the internet via DSL Modem connected via ethernet cable. Being that he is 1000 miles away, I am trying to diagnose via phone, could use some expert help:

System Info: Imac 17", purchased new around 2006- Intel chip, running Tiger OS

Symptoms:
Cannot connect via ethernet
-When searching system profiler, "Built-in Ethernet" shows up, but no MAC address
-In Network settings, he can see the various connection ports, but cannot check the box on "Built-in Ethernet" to turn the port on... won't let him.
-Wireless is not an option, I don't want to be 24/7 tech support

Diagnosis? I am thinking that the power surge may have fried the ethernet port on the motherboard.

Repair Solution: Planning on picking up the Apple USB Ethernet adapter. I know it doesn't have the correct drivers to run on Tiger, but found a driver online that claims it allows use of the usb adapter on Panther on up.

Questions- Does this sound like a fried ethernet port? Any other easy diagnostic tests I can do? Does the USB adapter sounds like a decent solution?