Оформил: DeeCo
Автор: http://www.swissdelphicenter.ch

// For some reason messages.pas declares no message record for this message 

type
   TWmMoving = record
     Msg: Cardinal;
     fwSide: Cardinal;
     lpRect: PRect;
     Result: Integer;
   end;

 // Add a handler to your forms private section: 

procedure WMMoving(var msg: TWMMoving); message WM_MOVING;

 // Implement it as 

  procedure TFormX.WMMoving(var msg: TWMMoving);
   var
     r: TRect;
   begin
     r := Screen.WorkareaRect;
    // compare the new form bounds in msg.lpRect^ with r and modify it if 
   // necessary 
    if msg.lprect^.left < r.left then
       OffsetRect(msg.lprect^, r.left - msg.lprect^.left, 0);
     if msg.lprect^.top < r.top then
       OffsetRect(msg.lprect^, 0, r.top - msg.lprect^.top);
     if msg.lprect^.right > r.right then
       OffsetRect(msg.lprect^, r.right - msg.lprect^.right, 0);
     if msg.lprect^.bottom > r.bottom then
       OffsetRect(msg.lprect^, 0, r.bottom - msg.lprect^.bottom);
     inherited;
   end;