There are a number of Line following robot projects with schematic and code for PICs on the Web, do some searching. A big advantage of PICs is the interchangeability of one for another. Most of the PIC based Bots I've seen on the Web use the 16F84 PIC. It would not be difficult to change to a 12F629 (if it has enough pins). Just read the data sheets for both PICs and change the code.
Once you have specific questions please ask.