In this instructable, I will explain how to use I2C on the Pi, with the examples of the CMPS03 compass module and SRF08 Ultrasonic range, using python. I will explain right through installing the OS, to ensure that the dependencies and everything is installed.
I2C is a communication bus designed by Philips, for chips to communicate with each other on a PCB. It is commonly used, however, for connecting sensors, such as the two examples later in this instructable and port expanders, because you can have multiple devices on the same two pins.
Step 1: Install R-Pi Image
Go to the Raspberry Pi website, and download the latest Raspbian image and follow the instructions burn it to the SD card.
There is an easy setup guide on the wiki, just follow it through.
When you have got it installed, run the config tool, and get everything going nicely. In my case, I am running it headless via SSH, which is enabled as default, at firstname.lastname@example.org.X (check on your router to find the IP).