emooney,
The comm_write.cgi command sends a string out the serial console. You must open up the camera and connect to the serial console within. Once connected correctly you can bring the 3 wires out of the camera and connect to your Arduino. Be aware that the Arduino is a 5V device and the camera is a 3.3V device so the Arduino's TX line will need diode isolation and a pullup resistor to 3.3V to avoid damaging the camera.
Read the wiki on this site
HERE and
HERE for some help on connecting. There are also many posts on the topic of serial connection such as
HERE. There also good instructions
HERE. There is info on diode isolation of the 5V Arduino from the 3.3V camera
HERE.
Good luck and be sure to share your results.
P.S.: When I experimented with the comm_write.cgi command, the serial sent out some error message but, IMPORTANTLY, it also sent out the text sent in the comm_write.cgi command, enabling your Arduino to monitor and react to the cammand.