its vibrating at the light cuz its old. And its doing this while its in gear because the engine wants to move the car, and the 'still' car is resisting the engines effort to move (which is rather weak since it's idling). When you put it in N, the engine is no longer being held back by something, its free spinning and not being stressed anymore. The reason it vibrates more when u put the windows up and down, or turn on your headlights for that matter, is also becuz you are asking the engine to lend power to something else (alternator), which just puts a little more stress on it. It's old, I think you are pretty much going to have to deal with it. I'm not sure about the 'not knowing its in park' deal, some sensor or something is worn it seems.