need advice on voice activated robot

Hi,
I want to make voice activated robot . voice sensor that get voice from particular person and work on certain operations

when i speak go forward
it should go forward

when i speak go backward
it should go backward

when i speak go left
it should go left

when i speak go right
it should go right

i want to use avr microcontroller series i am not sure but can i use atmega 16
and i also need voice sensor please suggest me
thanks