Check first where the leak is coming from. Check the top of your radiator and under it. Then your hoses and your water pump. These are just the places where you will find the leaks.
Fix this first and check your heater again. If heater still doesn't work, then check the heater coil.
first of all which motor? If its the 3.4 liter check next to the powersteering pump and under the t-body. Also if you can, look underneath, at the back of the cylinder head. And definitely check the water pump. let me know if you find antifreeze at any of those spots. Worst case scenerio its the head gaskets.