This guy built a motion sensing water gun to scare off the rabbits intruding on his garden. His goals for the project were:

# Must have automatic fire ability
# Must be able to detect motion
# Must be able to record the event
# Must be able to turn off auto fire mode and take on manual control
# Must be able to "Water the Lawn"
# Must be able to cover a 30 foot field of fire
# Must have a range of about 25 to 35 feet
# Must have the ability to work at night with all of the above features
# Must be able to Play back any recordings and laugh while sitting on the deck drinking a beer.

For supplies he used:
# X10 120 volt outlet
# X10 Transmitter and Receiver
# X10 Libraries that would work with C#
# In ground sprinkler solenoid
# Phidget single servo board with servo
# Phidget C# libraries
# PVC pipe, Copper Ice maker pipe, and a few other plumbing parts
# Old computer, 1.7 GHz with a gig of ram
# USB Web camera

He also used AForge.NET which is a C# framework designed for developers and researchers in the fields of Computer Vision and Artificial Intelligence - image processing, neural networks, genetic algorithms, machine learning, etc. http://code.google.com/p/aforge

Awesome project! I want one.