IMCA racing isn't about flying down the streets at Long Beach, or winding through the chicanes at Watkins Glen. It's about sliding around the curves, and nudging your opponent into the wall. Watch out for oncoming cars on the figure-8. Quick Race is straightforward. Get in the game fast and get the mud flying.
Career mode is much more detailed.
You have to buy a car, enter a race series, and try to do well enough to gain a sponsor. The higher you place, the better offers from sponsors you'll get, and the more money you'll make from them along with your race winnings. You can then take your money and upgrade your car with better parts, or buy a different class of car entirely. Career mode is where the meat of this game lies. It takes a lot of patience and money to advance to the higher classes.