getting to Beijing city centre

Hi,
I will possibly be in BJ by the end of November and I should arrive after midnight. I have to go to 81 Meishi Street, Xuanwu District which is near Tienanmen square. Which is the best and cheapest way to get there? Can I get the train and then the subway or they will be closed at that time? And how cold will it be?? I guess pretty cold as it is here in Germany.
Thx everyone!!