2000 Nissan Maxima SE Temperature fluctuating and steam/smoke from engine. What's going on?

My 2000 Nissan Maxima with 92000 miles on it started smelling like antifreeze the other day while driving it and then some steam type stuff came out from the hood area. The temp gauge stayed within normal range, and I drove it home. A friend looked at it and said there was some sort of problem with a vacuum line for my a/c. (I had the a/c on when I started smelling the antifreeze and seeing the steam). He said it didn't look like a radiator problem. He said something looked like the line burst or something. There was antifreeze spewed all around the front of the engine compartment. The antifreeze level was normal in the reservoir.  Today, I smelled the antifreeze again but stronger. Then lots and lots of steam or even possibly smoke started coming from the hood area. This time the temp gauge went well out of normal range just before the high range and then back down to normal, going back and forth as I drove it home. Each time it would go up, there was more steam, when it would go down, the steam subsided. It did this while idle at lights, and while accelerating.  I'm not going to drive it again until I can get it looked at but that's not until this weekend. I'm kind of worried it may be something huge and expensive and wanted to see if anyone knows what could be the problem? I'm hoping something easy like a thermostat, but I have a feeling it's way worse than that.