Rule of thumb for any rwd car is that you will need to tune out oversteer. So, you'll want a stiffer setup in the front and generally softer in the rear.
This brings to mind another point about tuning for different drive layouts:
The key thing to remember is how weight transfer impacts the drive wheels. In a rear-wheel drive car, accelerating shifts weight to the rear: so the drive tires are getting more traction in this situation. However the front wheels have weight taken off of them during acceleration, which means reduced steering. The opposite is true during braking (obviously).
This is one reason you have to be careful about throttle and brake application when managing a turn. Too much braking on entry to the turn and you can offload too much weight from the rear causing an oversteer spin. At the same time you will overload the front tires and possibly exceed the traction limit of the steering tires, resulting in understeer. Do both at the same time and you will be in a slide, or worse, a spin.
For front wheel drive cars, the situation is a little different. Accelerating takes weight off of the steering tires while at the same time taking weight off the drive tires (since they are the same thing in front wheel drive cars). Again, the opposite holds true for braking. This is why front wheel drive cars are especially succeptible to understeer during acceleration. Having the engine hanging over the front tires makes the situation worse. During breaking you can experience understeer by overloading the already overweight front tires which can then easily lead to a quick-snapping oversteer because of off-loading the rear tires. .
Most camps agree that the best balance for handling is a rear-wheel drive, front or mid-engine car. In the right hands, a rear-wheel drive car can be more easily controlled since the drive tires and steering tires are on separate ends, allowing throttle and steering inputs to operate indepedently. The best way to practice this control is to use the loop on the training course. Unfortunately it's not a complete loop, but it's a good place to practice. The goal is to steer into the corner and control the actual direction of the car with the gas pedal. "Steering with the throttle" is a handy trick and once mastered can make a RWD car a fantastically precise weapon.
AWD drive cars are a bit of a mystery for most people. The best rule of thumb here is to set the suspension more neutrally front to rear, with a slight tendency for softer settings in the rear, and keep it generally stiff. AWD cars are very forgiving on a track. Give too much gas and they usually just slide (unless the suspension is unbalanced front to rear, or braking forces cause the rear end to come around). If you get into a slide all you have to do is let off the gas a little (not completely!) and you'll pick right back up.
With all these thoughts in mind, the best way to imagine how to tune (and drive) any car is to use the traction circle (excuse the quality..I'm no artist).
Every car has a traction circle. And every car can accelerate, brake, and turn. The way each car handles them is different, and you represent this by changing the size (diameter) of the circle in relationship to the other factors (ie. the circle changes size but the crosshairs representing accel, brake, and turning do not). If a car has more traction capability then the circle gets larger. It is possible, on one extreme, for a car to have so much traction that it could never accel, brake, or turn beyond the limits of that traction, so the circle would encompass the crosshairs in that case (and the car would never slide, skid, oversteer, understeer, burnout, etc.).
Now, since 99.999% of cars can exceed their traction limits in some way, you can imagine the traction circle as it is drawn here.
Anything going on inside the circle is considered traction. Put another way, the area inside the circle is the total amount of traction available to you. Anything going on outside of the circle is considered loss of traction.
If you accelerate beyond the limit of traction (ie. you move to a point directly below and outside the circle) then you will do a burnout. If you brake beyond the limit of traction (ie. you move to a point directly above and outside the circle) then you skid (or lock your tires). If you turn beyond the limit of traction, you slide. Enabling any one of these forces in one direction reduces the total amount of traction available to maintain control. Combining factors eats up the amount of available traction even faster.
When you add stickier tires to a car, you increase the size of the circle. When you add more power to a car, you essentially descrease the size of the circle (or increase the size of the crosshairs, depending on how you look at it). Your goal with suspension tuning is to ensure the maximum amount of traction within all four quadrants of the circle given any track situation. Your goal as a driver is to safely use the maximum amount of traction available at any given time.
Seems simplistic but if you dwell on it for a while, the traction circle gives you a fantastic mental reference for tuning your car. Just as you tune the ECU curve in NFS:U2 to offer the most power in the rpm range that you spend the most time, you want to tune your suspension to give you the most traction given the dynamics and purpose of the car you are driving (FWD, RWD, AWD, Turbo, URL, Drag, Drift, Sprint, etc.).
There are many, many other factors involved (eg. tire slip angles, friction, air pressure, temperature, camber angles, etc.) but NFS:U2 doesn't account for them so I won't go over it here. But you can bet you're grandmama's cookies that they designed the handling dynamics around the traction circle concept.
Hope that helps. Probably more than you wanted to know but I could write about this stuff all day long.
Cheers,
) then ayl give you the numbers aight...
glad youre here 
