I had a used car I bought back in college. Previous owner had smoked. Steam cleaned the $H#T out of it. The interior grey actually had a yellow hue as I discovered. Anyway, after that the smell was unnoticeable.
I have seen them use an Ozonator at work too. It creates ozone inside the car to kill any odors, etc. Watch out though as it is a respiratory irritant. You can't be in the car when you use it and you have to open the doors to let it dissipate before you go back in the car.
Thanks - I heard about the Ozone machine, any idea where to rent one or if there is a place that will do it for me?