I second the dehumidifier advice, ours has been a God send. Lukcily we brought ours from the UK (we lived in an old house back home so used it every so often in the winter!)we've got one that claims to do a three bedroom house over two levels, and we don't need to move it from the back hallway for it to be effective in all the bedrooms and bathrooms at the back of the house.
I'm a big believer in airing the house too, especially in the mornings after a night of having the fire/heat pump on. Blast the house through with some fresh air, then wipe down the windows, close them, let the rooms get back to an acceptable temp and stick the dehumidifier on for a while. Though the problem's worse in our house here, even back home in our double glazed, centrally heated old house we used to get condensation, so it hasn't been that big of a deal for us to have to deal with it here as well!