if you got an arduino mini and two standard servos you can make a little robo pet that walk on two 4 legs.
but in the project i didn't used a original arduino. i used an ATmega8 microcontroller with arduino boot-loader.
if you are a little familiar with AVR micocontrollers and isp programming you can turn your ATmega8 microcontroller into an arduino.
To load the sketch in to the arduino you need FT232 based device. but in the place i live im not able to get this. so i used a CP2102.
AS the ATmega8L microcontroller works from 3.3v to 5 v i didn't use any voltage regulator .
to power my arduino and servos i used 4*1.2=4.8V Ni-MH (2700mAh) batteries. some times these servos may cause Reset of the circuit as they draw more current. To prevent that i used 2*1000uF capacitors across Vcc and GND.
just by using few nuts, bolts ,3mm iron(any metal that can be bent) wire and 2 standard servos.
while bending the metal wire for legs make sure that all the legs are touching the ground properly
check my blog for more info and arduino code :