My 2000 impala is running hot, how can i determine the problem?

First check the coolant level. Then make sure the cooling (radiator) fans are turning on. There is a fan controller that governs when they come on, based on the engine coolant temp sensor. If not, then the fan, fan controller, or ECT sensor are suspect. Then make sure you have good coolant flow. If not the thermostat or water pump are suspect. (Thermostats are easy to replace, so start there.) You can squeeze the upper radiator hose when the engine is running to feel if its pressurized, just be careful as it can get hot. (wear gloves.) If it feels soft there is a problem with coolant flow, it may be something simple like the radiator cap not maintaining proper system pressure, or the thermostat, or the water pump. Finally you can check the overflow bottle and the hose running to it, any cracks will prevent coolant from transferring between bottle and radiator.