Help needed with a small custon job

[AlgernonUK]

Not sure if this should go here, as it's about development, or in the noob forum, cus I'm new.

I am building a NAS from a Mini ITX with an atom 525, and will be making a custom case for it.
Part of the case will be an LCD panel driven by an Arduino, which will show various stats.

So, I started up a shell, and tested a quick python script to output data to the arduino through serial usb.

Code:

import serial

mySerial = serial.Serial('/dev/ttyUSB0' , 9600)
mySerial.write("Woot")
mySerial.flushOutput

I'm new to python, but noticed that when trying to run this script, it didnt have the serial library imported.
So I downloaded and extracted the tar. And followed the instructions to install it
python setup.py install
only to be told that /usr/local/lib is a read only file-system

Is what I'm trying to do possible? And if so, how do I go about doing it?
Any pointers greatfully received.

Al.