95 Sls Heating Problem!! Please Help!

so today when I got in my car there was white smoke on the windshield and it smelled like coolant. I turn the heat on and it started to blow out white smoke (smells like coolant) and it blows it out like crazy and the windshield fogs up. When I turn the cold air on the smoke doesn't blow out anymore but when the heat is on its crazy. Anybody know what the problem might be and if its expensive to fix? Thank you.:shakehead

probablly a leaking heater core. Probablly cost $500-$700 to fix.

As 83 noted, a leaking heater core.