Has anyone done a heater core on a 2001 SSEI. I think mine has gone out and i need ur guys help if anynone has done one? I have done them on other cars but not on bonnies.

This link provides information on how to replace the Heater Core depending on your RPO code.

What makes you believe it needs replacing? Is it leaking?

I believe it is leaking it somewhere because the coolent level always is down and when i turn the a/c or heat on the inside of the car smells like coolant a very strong smell

Just a couple of signs that the heater core is leaking,

Water on the carpet, passenger side under the glove box.
A steamy mist on the windshield when the defrost button is set on the heater.

If you don't have those symptoms, check your coolant elbow from the LIM to the tensioner for leaks, as well as the radiator cap. Also, the water pump, and the lower elbow from the tensioner to the water pump. If no problem there, check for milky looking oil, or any white vapors from the tail pipes. Read up on this techinfo article. The upper intake will not be relevant - as your supercharger takes its place. But you are just as prone to the LIM gasket problem.
http://www.bonnevilleclub.com/forum/...e=article&k=38