I'll give you an example of foreshortening. Go look at my gallery. Find the Audi S1. Notice how I drew the whole front of the car, but the side of the car is really short. I had to draw the wheels, windows, the door all really tall and very narrow. Thats foreshortening.
The link you showed me was pretty sweet. although, I think the problem with it is that the lines which are supposed to be parallel arent. Like the top of the windscreen should be parallel with the bottom of the bumper. Its hard to explain what else makes it look sorta weird. I cant really give you any advice, other than keep drawing. My cars used to look really really crap like 3 years ago. My parents were supportive and would tell me they werent very good, but I should keep working on them. So I did, because I loved to do it. and now you see what my cars look like. They arent perfect yet. I'm not sure they ever will be. But I'm definitely much more proud of them now than I used to be.
Plus, you might want to try copying pictures of cars. That way you draw what you see, not only what you imagine. THe more you draw what you see, the easier it will become to make cars look realistic with perspective and foreshortening without having to look at anything. Most of my good car pictures are copied from a photograph. I dont trace, but I get very picky about lengths and distances. I've gotten to the point where I use a ruler to measure almost everything. I think it might have something to do with the engineering graphics classes I'm taking. Oh well. I've rambled on long enough.
Keep up the good work.

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Santa Claus wears a Red Suit, He must be a communist. And a beard and long hair, Must be a pacifist. What's in that pipe that he's smoking?
- Arlo Guthrie