If public transport is a city in Belorus to you, take a cab - 40$ as of summer 2012

Marta version 1: Drop-off bit further away from the house, bus #36.
Buy a ticket at the airport.

  from airport any MARTA train to Midtown station
take bus #36 (every 30 min)  
ask driver to drop you off at VIRGINIA AV / Highland AV intersection
cross the road, go up VIRGINIA AV (it curves)
 TURN LEFT onto ROSEDALE ROAD
  Up on the right, white mailbox: 979 Rosedale Road

Marta version 1: Drop-off bit closer to the house, bus #6 sometimes more frequent, but one extra train change

  from airport head NORTH on any MARTA train to Five Points
remember to get bus TRANSFER at the turnstile
change to eastbound MARTA train
get off at CANDLER PARK
take bus #6 NORTH (every 15-30 min)  
after you get on BRIARCLIFF, ask driver to
drop you off at VIRGINIA AV (on your left)
cross the road, go down VIRGINIA AV
 TURN RIGHT onto ROSEDALE ROAD
  Up on the right, white mailbox: 979 Rosedale Road