display - How to trick windows 7 to use only a part of the screen

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How to use only part of screen, as if the monitor was a smaller one?

I have a broken 20" LCD monitor which displays random pixels in the top 200 lines of pixels. I want to limit the display in such a way that when I maximize a window it will not be in the bad area and to limit the cursor position so it won't be in the bad area.