the thing your dad is worried about is condensation... i'm supprised no one and droped that word yet. u dont have to worry about that in this situation.
when you bring the computer in from the cold, the air immediatly next to the case gets colder (by convection heat transfer). This is good because it means the case is getting warmer. but the problem comes with the psychrometric (meaning air-water mixture) principle that, all things being equal, cold air will hold less water vapor that hot air. Here is a psychrometric chart: http://www.sp.uconn.edu/~mdarre/NE-1...ric_inset.html
if you take the time to read it, u will see that a room at 70*F and ~60% relative humidity (a reasonable room temperature), the air will be saturated (100% relative humidity) with water vapor at ~50-55*F. so if the air around the computer gets colder than 55*F, condensation will begin to form on the computer because it can no longer stay suspended in the air.
this principle can be demostrated by taking a can of beer (or pop if you're underage) out of the fridge and setting it on the counter top. as the can warms, the air around the can gets colder. the water vapor in the air cannot be suspended any longer in the air and has to go somewhere. it 'condensates' on the side of the can as that is the coldest place.
if the circuit boards in the computer have condensation on them, they can short circuit ESPECIALY WITH A LARGE AMOUNT OF DUST ON THE BOARD! this will ruin your electronics!
in short, Father knows best! lol