const char *mutexname = "mtxUIV2";

//--------------------------------------------------------------------------
WINAPI WinMain(HINSTANCE, HINSTANCE, LPSTR, int)
{
//-----------------------------------------------------------
        HWND hMutex = CreateMutex(NULL, true, mutexname);
        DWORD LastErr = GetLastError();
        if ((LastErr == ERROR_ALREADY_EXISTS)||
            (LastErr == ERROR_INVALID_HANDLE)||
            (!hMutex))
         {
          MessageDlg("Программа уже запущена",
                        mtError, TMsgDlgButtons() << mbOK, 0);
          exit(1);
          return 1;
         }
//-----------------------------------------------------------
        try
        {
                 Application->Initialize();
                 Application->CreateForm(__classid(TMainForm), &MainForm);
                 Application->Run();
        }
        catch (Exception &exception)
        {
                 Application->ShowException(&exception);
        }
        ReleaseMutex(hMutex);
        CloseHandle(hMutex);// по совету BoundsChecker'а :)

        return 0;
}