If your lucky it is a leaking heater core, or hose to the heater core at the fire wall. The general rule of thumb is white smoke is coolant burning or leaking, black smoke is rich fuel not burning all the fuel and blue smoke is oil burning or if you have a turbo the turbo could be burning oil.
To find whats leaking under the car put a piece of cardboard and see where it is leaking and what color it is, black will usually be oil or if you have auto trans then it would be reddish (unless it is really old or burnt. Oil leak under the radiator area could be trans. line leaking at the trans cooler or the power steering rack could be leaking they both use reddish fluid so you will have to figure it out