If you haven't seen the maya 6 presentation, someone of the alias guys build such a rig for a viper. He used dynamic curves for that... looked cool and the behavior was not bad.
The problem when using things like springs is, that they are really hard to get under control. When ILM they worked on the pod racer in star wars episode 1 they used maya dynamics, someone who has done this told me that with the next revision they had a bug in it and it didn't work since this release...
If you wanna use custom code, on one of the game developer (I think it was www.gamasutra.com
) someone wrote an article about rigging and simulating cars.