Try being gentle on the gas, don't push it down too quickly, try a more gradual approach. Don't apply too much throttle when turning, in fact, for a start it would be a good idea not to apply any throttle before your steering wheel is completely straight. The best tip, however is: practice, practice, practice .
edit: errm, are you using a wheel at all? because with keyboard it's much harder to control the powerful cars, I hear.
You just have to be easy on the throttle. If you racing with keyboard then try turning on traktion control. You can't apply 100% throttle right away, the more powerful the car the more careful you have to be with the throttle.
there will hopefulyl be a traction control at some point during the game, the throttle help aint really traction control it just helps you a tiny bit with how much power you put down. but no where near "traction control" standards
I'm using mouse/keyboard at the moment (can't afford a wheel ) and I can tell you that throttle help is useless with RWD cars.
At the moment I'm limited to using FWD or AWD cars otherwise I spin as soon as I apply the throttle. The only exception is the FO8 at Kyoto Oval where things are fine once I'm up to speed.
I'm just looking forward to the end of unemployment so I can buy a wheel!
I drive a wheel but i used to drive a mouse. best advice i can give is turn "button rate" to the lowest level, and "pump" the gas key/button to keep below full throttle. also, i found that mouse = steer + a/z = gas/break gives better control than all controls in one hand (mouse).
Are you sure? The FZ50 is very heavy, and it has only road-super tires, which means speeds are low and throttle/brake/steering inputs make little immediate difference. You can jerk the wheel all over the place without anything happening. Well, sort of. At least a bit of slip is a good thing, and you really have to make a dozen mistakes to lose the car completely (unless you forget to brake soon enough).
The FO8, on the other hand, has so much power, and it's so light, that there are many, many, many places where full throttle is simply not an option, but you need some throttle to keep your speed and downforce up. There is almost no slip angle to play with, so steering inputs have to be absolutely precise.
Using a mouse and keyboard, I have no trouble controlling the FZ50, and I have no trouble doing competitive lap times with it (two WRs). The FO8, however, is almost impossible to drive at any speed without some form of variable throttle. The only hope is to use taller gears than you would normally and bog the engine out of corners.
So, anyway, to control a RWD car, such as the "fast" XR GT Turbo (it's actually the second-slowest RWD, generally), you don't need to be light on the throttle (unless it's the FO8). Simply counter-steer when you know your rear end is going to be coming around. Don't wait until you lose it. Start pulling to the outside of the corner as you put on the throttle.
It's all about weight distribution. If your car is leaning to one side, and you hit the throttle, the rear end is going to come around. Period. By counter-steering, you rebalance the car; if you counter-steer suddenly and violently, you can induce some understeer, which can put a sudden end to the oversteer. Be sure to center the wheel again as soon as you can, though, or you will start sliding in the other direction instead.
The thing about the FZ50 is that it's so damn heavy, it takes a full landing strip to get it to stop. I just hate that car. On the other hand, the GTR version of the FZ50 is a charm to drive. I still suck and get it to spin for really small mistakes I make, but that car is the best drive around.
I drive with a Logitech MOMO Racing wheel. Cost me 125$ CAD. Only thing I have against it is that after having it for only three months, it already starts to feel like it's grinding or something.
I'm currently using my old Saitek r440 Force (version 1) - its a cheapish wheel (about £40) - but the pedals are amazing! I've hammered it for about 4 years (+ my 4 year old step-nephew gives it a good hammering at least once a week) and whilst the wheel is a little worse for wear, the pedals are still in perfect condition, which is more than can be said for logitech's.
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) and I can tell you that throttle help is useless with RWD cars.
Well, sort of. 
