Here it is a great tutorial on how to interface PS2 with any MCU. There you can find all necessary information that helps you to set up various embedded projects that include PS2. These include Wiring information, Low level signal analysis, packet information disclosure, Complete Command listing and explanations and finally sample application examples with PIC18F4550.
There you can find two programs that reads PS2 Dual Shock or Guitar Hero controller. The first program will configure a controller in analog mode so that all the joysticks and button pressures can be read. It also sets up the Left pressure to controller the left vibration motor and the Right button pressure to toggle the smaller right vibration motor. The second program can operate in two modes: Continous SPI to Serial and Bulk Capture and Dump. Happy sniffing.