If the car is 4wd adjust the VCD to a lower number to make the car more like a FWD so it doesnt spin as easy when you accelerate on gravel or snow. It wont turn well on tarmac but will control the over steer on loose surfaces.
If the car skates to the outside of the turn when you steer then your either going too fast OR your suspension is set too hard. Its a much finer line to set up a rally car...when you brake you need to get a lot more of the weight over the front wheels but if theres too much you will push through the grip limits!
Alot of this is down to spring hardness settings...As a general rule cars that drive on loose and bumpy surfaces have a much softer spring rate than tarmac track cars. If the track is very twisty drop the gear ratio quite a bit. When setting the brakes up put around 80% on the front and 20% on the back....on gravel you will still be able to make a car powerslide since the grip is poor and the back end will "come out" with very little braking......specific settings depend on the car you are driving....If its already rally spec the suspension should be near enough. that just leaves the brakes VCD and diffs to play with.
Hope this helps im no expert this is just my own experiece