Coolant leak from under dash

I have a 1993 pontiac bonneville sse with 176000 miles. Yesterday on the way to work, my windows fogged and steam/fog started coming out of the air vents. Also, I recognized the distinct smell of antifreeze. When I pulled over I discovered that a drip coming from under the dash on the passenger side. A coworker told me it was most likely the heater coil and it would be expensive to have replaced. Is this something I can do, if so where do I get instruction? Thanks, Wayne