Building the Robot - Ardbot
The robots are based on the chassis kit available at Budget Robotics.  The kit is called the Ardbot.  You can find out more info about the kit here.  Building instructions are available here.
picture from Budget Robotics Ardbot building Instructions.

Adding Sensors
Sensors are added to the robot to provide input for navigation.  A five part series called Making Robots with the Arduino by Gordon McComb in Servo Magazine from November 2010 until  April 2011 provided the choice of sensors, how they should be mounted to the robot, and the wiring diagrams to connect the sensors to the Arduino (part 1 - Servo Magazine, November 2010, p. 56).  

Programming the Robot
The robots are programmed using Modkit.  Modkit is a programming environment that is based on the programming language called Scratch.  Scratch was developed by MIT's Kindergarten Labs.  It's purpose is to make programming accessible to children. In order to use the motors in Modkit, I had to become a member of the alpha club.  Servo control is not included in the free version of Modkit.