When you say ovrheating, do you mean it is warm in your lap (not a huge problem) or is it shutting down from being too hot (big problem!)
Batteries get hot when they charge from a low charge state. Could be the sign of a failing battery if your battery life is very short.
CPU gets hot if the fan and heatsink system are not operating properly. Check to see that the fan turns smoothly. As another has suggested, blow out any dust from the fan area but hold the fan blades, over spinning the fan could be bad. Also, perhaps the thermal paste between the CPU and cooling system is inadequate. You may want to dissassemble and re-paste the junction.