Send EM_SETSEL message or use Edit_SetSel macro defined in windowsx.h.
Code:
   SendMessage(hWndEdit, EM_SETSEL, (WPARAM)3, (LPARAM)3);
   SetFocus(hWndEdit);
or
Code:
#include <windowsx.h>
// ...
   Edit_SetSel(hWndEdit, 3, 3);
   SetFocus(hWndEdit);