Our windows have actually already been sealed--we mentioned the cold to the landlord and he had one of the building maintenance guys come around and put plastic sealant on our windows, which did help some but not a lot.

Part of the problem (and why our bedroom is so cold) is while the living room aircon unit has a wooden wall mounting that it sits in, the bedroom one was apparently just shoved into a hole in the wall that makes it almost impossible to seal all the cracks in. We mostly just kep the bedroom door closed and stuff a towel in the crack when it gets too cold, but that doesn't make it easier to get up in the morning. :-\