ok firstly, what kind of electronics level are you starting off from? GCSE, A-level, just doing it for fun??
i replyed to an earlyier post about ultrasonics so you may want to look at that.
basicly i made an ultrasonic range finder last year, the results wernt brill but the basic method was sound. for my report i compiled a list of ways to improve it, so i could give you some pointers and sugestions if you need.
PIC knowlage is v important for this project, i started with no PIC knowlage and that set my project back alot!
if your new to pics i sugest the 16F684 from microchip