Does anyone know what it is that gives a new car that new car smell?
How can I get that smell in a 1990 model car that smokers formerly owned?

It's the outgassing from the plastics - and in some cases leather.

At Wal-Mart, you can actually buy "New car" scented spray. I tried some though at the store, and it smelled bad. :( You'd have to go look around and try some yourself.

If the car was heavily smoked in, I'd reccomend Febreezing the hell out of it. And then maybe try some air fresheners.

I say see if they have some Gasoline Scented air freshners, its the only thing that over powers the nasty smoke smell. Plus gas smells better.

Shampoo with disenfectants and use live enzymes to remove the odours. Enzymes are cool little organisms that feed off of odour sources. The stronger the source the harder they work. I originally used them to remove smells from sumps and water traps and found they work great in a shampoo mix too. Make sure after you shampoo to let the carpets seats and headliner are dry other wise youll have a new smell "mildew"
When a car is smoked in for years its a good idea to clean the windows and vinyl/leather with good interior cleaners that sanatize. Also spray the vents and blow them out. It can take alot of time but it does go away when you clean the living hell out of it.

I've read that taking a container of coffee and leaving it open in your car will absorb smell.

I've read that taking a container of coffee and leaving it open in your car will absorb smell.
Good trick but it stales your coffee :(