Let's Make Robots!

need some help regarding basics!!

hello everyone.. well i m a very new but enthusiast member of this society. well i need some help. well initially i want to make a simple obstacle avoider ,working on differential drive algorithm and using photoresistors. i wish to know that how should i decide that which will be the best motor for the wheels which i want to have 8 c.m. diameter. and do i need to go thru some books on any purticular tutorial in programming before i start with it. plz reply.