BOOL MoveWindow(
  HWND hWnd,      // handle to window
  int X,          // horizontal position
  int Y,          // vertical position
  int nWidth,     // width
  int nHeight,    // height
  BOOL bRepaint   // repaint option
);

This cud be used in the WM_PAINT event section and in 
WM_INITDIALOG section.

WM_SIZE message is received by the window procedure when a
user resizes a window. In order to limite the size of a
window, you could handle the WM_SIZE message appropriately.

WM_SIZE message to an application is posted after the 
resizing operation, instead WM_SIZING should be handled and 
the lpRect member can be modified.