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There are (as far as I know) some third party alterations floating around on the internet that are known to change it to windows mode, but for obvious reasons we cannot support such a modified game executable.
Try looking around the Modding subforum, a fan wrote a little program to allow you to play in any res.
As jpd mentioned, this is third party and Paradox is not responcible for it, or any problems you may encounter with it.