The heart of this project is an Arduino Duemilanove microcontroller, equipped with an Ethernet adapter, and a home-made circuit that connects it to power switch on his computer. The Arduino is always on, so at any point in time (and from anywhere in the world), He can command the Arduino to start up his computer.
The power switch control circuit uses a reed relay to short out the power switch pins on his motherboard. He installed a jack in the back of his case, which gives him access to the power pins from the outside. He tapped the wires from his case power switch, so that the front panel power button still functions.