Actually i believe admin has some tutorials for this..
BUT.. you have a lot of options.
First of all, what microcontroller do you have? Do you even have one? If not, go check out the 50$ robot tut. It uses a decent enough MCU.. even if the memory is limited. Thats going to be quiet the hurdle for mapping. Unless it has some non-volitate memory(stuff that remebers after powered down) your going to have to remap every power up. Which may be fine! Also, you will eventually run out of space..
Tell us what microcontroller you have, and we can go from there.
part list:
microcontroller
something to move the robot
Panasonic IR Range finders(cheap decent solutions)