Some time ago I've found on the web this really cool but outdated tutorial: https://www.sparkfun.com/tutorials/304
I've ported the code to Python, because OpenCV is only maintained for C++ and Python.
The results can be found here: https://dl.dropboxusercontent.com/u/1542785/PanTiltFaceTracking.zip
Hardware and arduino software should be done according to the original tutorial.
For Python part I assume that Linux and Python are installed and other prerequisites can be obtained using:
sudo apt-get install python-numpy
sudo apt-get install python-opencv
To run the program simply type:
Administrative privileges are needed to access arduino serial port. In case when a wrong camera is used just change the first argument in "go" from 0 to 1...