With a new physics engine you can no longer just gun it at full speed and expect to make every corner. Now that it's more realistic it takes more skill to drive in gta4 especially early in the game.
First of all if you know how to drive in the first place, its a lot easier to understand ho to drive in gta 4. Just like in real life; you need to slow down before you take a corner. Brake with your regular brake, then tap your hand brake to finess your turns.
Step2
If you handbrake and hold down the accelerator the entire time you can drift. however this can be harder in slower lower quality cars.
Step3
It makes a big difference what car you're driving, just use common sense. Force is equal to speed times mass. So if your driving a big truck or hum vee at top speed don't expect to get phased by other cars on the road. Also if your driving a family sedan take it easy on the corners.