SetWindowLong( hWnd, nOffset, nValue ) -> <nOldValue>
------------------------------------------------------------------------------


 PARAMETER:

  <hWnd>        Is the handle that identifies the window

  <nOffset>     specifies the zero-based byte offset of the value to be 
                retrieved. Valid values are in the range zero through the 
                number of bytes of the extra window memory, minus 4 (for 
                example, if 12 or more bytes of extra memory was specified,
                a value of 8 would be an index to the third long integer).
                You can also use these predefines constants:

                 GWL_EXSTYLE   -20 Extended window style 
                 GWL_STYLE     -16 Window style 
                 GWL_WNDPROC   - 4 Long pointer to the window procedure 

                The following values are available, when the function is
                called for a dialog box: 

                 DWL_DLGPROC   4 Specifies the address of the dialog box
                                 procedure
                 DWL_MSGRESULT 0 Specifies the return value of a message 
                                 processed in the dialog box procedure. 
                 DWL_USER      8 Specifies extra information that is
                                 private to the application, such as 
                                 handles or pointers. 


  <nValue>      specifies the long value to place in the window's 
                reserved memory. 


 RETURNS:

  The return value is the previous value of the specified long integer, 
  if the function is successful, or zero, if not.


 DESCRIPTION:

  The SetWindowLong function replaces a long value at the specified offset 
  in the extra window memory of the given window with a new value.


 SOURCE:  

  SOURCE\WINAPI\WNDIS.C