Nope, it is the same driver. But what I also did was updating the bootloader and that helped me a lot. From http://arduino.cc/en/Main/ArduinoBoardEthernet
If you want to use a FTDI cable to download your sketches on the Arduino Ethernet, please refer to this guide: Upgrade the Arduino Ethernet bootloader to the latest version
but you'll need a second arduino (ethernet).
follow the instructions on this page:http://arduino.cc/en/Main/ArduinoBoardEthernet
when finished. disconnect and reconnect your upgraded arduino with your USB2serial light cable and try to upload blink sketch to your upgraded Arduino (still selecting Arduino ethernet.