Gaskets leaking oil ?

Hi! I'm new to this group, but I have a 97 Pontiac Grand Am and it's automatic with a V 6 engine and that's all I know cuz I'm a girl lol Well yesterday my car overheated and one of the radiator hoses exploded, so I bought a new hose and had my friend put it on ( my mechanic is my friend ) and he said it was overheated most likely because one of the radiator hoses had a leak, and it was an old hose anyway. I know it wasn't the radiator cuz I bought and had my new radiator installed like last week. Well after he replaced the hose, he said he assumed that the thermostat was already new, because the lower hose was brand new, so he felt like the car dealer probably renewed both since the hose was new, so he ran the car for a while to see how it reacted, and all of a sudden this smelly steam stuff started coming from under the engine, and out of the tail pipe there was a LOT of smog coming out, so he said he thinks it's a gasket something, something about the gaskets cooking the oil or something and that they needed to be changed, because the engine oil is still full it's not even low on oil or anything. Could someone help me understand this and maybe tell me what you think? and also, how much normally is labor for replacing gaskets? Thanks!
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replacing head gaskets is expensive...the actual part is cheap but the labor is a lot..i was told 1200 by one of my past mechanics...they pretty much have to pull the engine out or apart or something? i dont know the complete process but i know it's a lot of labor....i wish the best of luck to you :-/