I've made a prototype of a line following sensor so I should be uploading information on how this works in the next few weeks. It will eventually be used as an input into the PIC which controls the autonomous robot.
I used a design from ikalogic.com which can be found here. I chose this design as it requires very few parts which means a large number of sensors can be created very easily and cheaply.
Assembly of the line following sensor was very easy, I followed the instruction here and I was able to put a test assembly together very quickly. Below is a picture of the completed board with the wires clearly visible.
Here is a quick video showing the homemade line following sensor in action: