I know this works in a car, but if you can get hold of any of those little silica gel packets that usually are found in things like trainer boxes etc, they soak up any moisture around..not sure how many you will need tho...
Actually thinking of it, not the best of ideas but try it in your car...
A small bowl of salt in the room does the trick. Use to use it in my caravan years ago, a bit sad but it does really work!
rubbish is'nt it!?!
You should NEVER use a de-humidifier in a newly plastered room. It makes the plaster dry too quickly which can cause cracking.Is your house new / recently replastered? I'm not a builder so you might want to double check this... but I believe that new plaster takes a very long time to dry out completely and releases it's moisture into the atmosphere. If this is the case, then a dehumidifier would be a worthwhile investment as it could help to dry the plaster out quicker.
Also, from experience, sometimes leaving the curtains open during the night can lessen the condensation on some windows.