the Accelerometer will give o/p the value(voltage) will be in analog form you need to use ADC, since the avr microcontroller has inbult ADC you can use that…. here i am sending you th elink for AVR ADC
http://www.engineersgarage.com/embedded/avr-microcontroller-projects/adc-circuit
since u have 3 values you need to select one channel at time… compare the value through you calibrated one and you can find the direction/till,ect for you object….
nice project all the bst….