Fully automated sentry BB gun, anyone?

The idea of this project was to create a fully-automated sentry gun, capable of picking out a human target and accurately tracking and shooting him or her in the heart. Really, the idea was to find a cool robotics project for the summer while I was working at an advertising agency, and I'd only ever seen sentry guns in movies (like Congo) and video games (Half-Life 1, Half-Life 2, Team Fortress Classic).

So what if the list of useless guy-projects I have is getting long? Building this stuff is half the fun!