@Nathan Gesner
If it is a severe case, there isn't much you can do because it seeps into the dry wall which may mean your best plan of action is to replace it.
Basic Steps for a chain smoker:
1A. If the walls don't use latex paint, use a product TSP to clean every inch of the walls (be sure to use proper protection & ventilation).
You can also try a natural mixture of ammonia, white vinegar, baking soda & extremely hot water.
1B. If the walls are painted with latex paint, DO NOT USE TSP as it will do more harm than good. Instead use a strong detergent like Mr. Clean or Fantastik.
2. Then use a cleaner like Orange Cleaner or L.A.'s Totally awesome and scrub the bad areas (both available at Dollar stores and actually pretty helpful here)
3. Once the wall surface is completely clean, paint on Zinsser's BIN or Coverstain Primer. KILZ is cheaper, but not as good from my experience. The more coats, the better chance of getting a complete seal. Typically 2 is good if you know what you're doing, 3 if not.
Here are a few additional methods I'd look at if it was an extreme case:
-Replace all soft materials in the house (carpet, drapes, etc.)
-Have the HVAC unit cleaned out and use
-Rent an Ozone or hire a company to clean the air
-Replace the drywall all together
-Another option is to clean, paint with KILZ (removing most of the odor but not all), and to simply market that unit as a smoking unit.
Hopefully this helps Nathan