Need to include:
import serial
To get a module called not Serial but PySerial.
This doesn't come with most python installations, but it's quick to download installers, as demonstrated in this adafruit tutorial:
https://learn.adafruit.com/arduino-lesson-17-email-sending-movement-detector/installing-python-and-pyserial
Which gets the installer from here:
https://pypi.python.org/pypi/pyserial
Here are a couple of really nice forum threads containing example code:
http://stackoverflow.com/questions/676172/full-examples-of-using-pyserial-package
http://stackoverflow.com/questions/1093598/pyserial-how-to-read-the-last-line-sent-from-a-serial-device
