Windows 7 & 8 will automatically remember the current size of a window when it is closed. If you open Microsoft Word and make the window larger or smaller, it will save that setting when you close Word. All windows will remain that size until you change it and close again. If the window is not re-sized properly when the application is reopened, then try the steps below.
To force Windows to record the size of a window and set it as the default size for that program each time it's opened, simply re-size the window to your preferred size, then depress and hold the CTRL key while you click the red X to close it. The program should use that size as the default size until changed.
From answers.microsoft.com - (discusses Internet Explorer 8 but works for all programs under Windows)
Keywords: Windows, default window size, resize