Very good points being made. Its all about controlling the kenetic energy in your vehicle. Time for a quick refresher in HS Physics.
Kenetic energy=stored energy that is being held at bay.
when driving in snow, ice, or any other slick surface, the driver must pay attention to what is ahead. You have to anticipate the motion of your truck long before you actually have to make any directional/speed changes.
Say you are cruising along at a respectable 30mph (hey, its slick out there). You have no throttle or brake imput. You are just gliding along. You reach a curve in the road. Before you enter the curve, you begin to apply brakes (to slow it down) and then turn the wheel (to follow the road). However, that nice glide you were enjoying was full of kenetic energy. That is...the truck still wants to go straight at the current speed. By affecting both aspects of this energy, you are putting lots of pressure on the tires to affect the changes. With the slick surface, they can not cope and you begin to slide.
The proper way to do this is to slow to the appropriate cornering speed before you actually enter the curve. This way, you are slowly bleeding off the momentum energy while leaving the directional energy in place. Thereby, reducing the stress on your contact patch. Once the speed is reduced, that new energy is left in place. You then begin to turn the wheel affecting the directional energy. This way your tires are only affecting that one bit of kenetic energy, thereby making them work less at maintaining traction. After the completion of the turn, begin to head back to cruising speed.
And, most importantly 4WD ONLY MAKES A DIFFERENCE IN GETTING GOING. BRAKES WORK THE SAME AS A RWD SPORTS CAR. That being said, don't go plowing past others on the road cause you have the stability to go faster....cause you may still have to stop suddenly to avoid grandma blue hair in the Ford Explorer.