You would only have hope of running Windows XP via an emulator. Even then, running a full XP OS would drain your tablet/phone battery since the emulation would be quite CPU-pegging (100%).
You might get away with porting Windows CE 6/7 to a high end android phone, problem there is that you'll need to make your own drivers for the hardware. And besides, Windows CE is like a really stripped down version of Windows 95 for mobile devices... even the CE version of Internet Explorer 6 can't render things properly.
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