I smell coolent and see that it is wet under the plentium on my 4.6 engine . What could be leaking under their and is it much trouble to fix it ? Thanks

 

Could be a number of things. Loose intake manifold, bad intake manifold gasket, bad heater hoses, loose heater hose clamps, or the dreaded metal recirculation tube. See attached pic.

 

Hope this helps, if it turns out to be the tube under the manifold. "http://www.youtube.com/watch?v=BazXM2y_M0Q", Youtube has several videos on various coolant leaks in GM's.
Also, if it turns out to be the piece under the manifold there is a way to repair it without removing the manifold by simply using heater hose, clamps, and a 90 degree elbow to reroute it from behind the water pump to the heater core.