private
  
procedure WMSysCommand(var Msg: TWMSysCommand); message WM_SYSCOMMAND;

  {...}
implementation


procedure TForm1.WMSysCommand(var Msg: TWMSysCommand);
begin
  if ((Msg.CmdType and $FFF0) = SC_MOVE) or
    ((Msg.CmdType and $FFF0) = SC_SIZE) then
  begin
    Msg.Result := 0;
    Exit;
  end;
  inherited;
end;