johnwasser:
Did you connect all the other data pins? Power? Ground? Check the Ethernet Shield schematics to see which Arduino pins it connects to.
I didn't connect the other data pins, I did have power and ground connected. As I said, this setup worked when pin 10 on the Arduino was connected to pin 10 on the Ethernet shield. So I see no reason to hook up other pins. All I did was change 5100.h and recompiled and uploaded to the Arduino. Physically, I moved the wire from pin 10 to pin 8 on the Arduino.