Re: 1992 Taurus White Smoke Under Engine Plus ....
how many miles? what engine? you might have just squandered $500 - but it could have been worse. Did you drive the car before you bought it?
Head gasket would show as oil in the water or water in the oil (more likely) with coolant loss and overheating. Run the car ( if it still runs) for a while, then take off the oil filler cap. If there is a milky brown goo on the cap, that's bad. Pull the dipstick. If the oil looks like a chocolate milkshake - bad too. Look in the coolant reservoir - oil or black stuff in there? Bad.
Using a lot of coolant? Bad. Overheating until the engine clanks and coughs, seizes up and dies in the middle of rush hour traffic - bad.
Good luck - need more info ( engine, miles etc...)