uses
  OLECtl;
var
  OCXHandle: THandle;
  RegFunc: TDllRegisterServer;
begin
  OCXHandle := LoadLibrary ('C:\Windows\System\custom.ocx');
  RegFunc := GetProcAddress (OCXHandle, 'DllRegisterServer');
  if RegFunc <> 0 then
    ShowMessage('Error!');
  FreeLibrary (OCXHandle);
end;