struct ProcessWindowData
{
	HWND hWnd;
	unsigned long lProcessId;
};

BOOL CALLBACK EnumWindowCallback(HWND hWnd, LPARAM lParam)
{
	ProcessWindowData& wndData = *(ProcessWindowData*)lParam;
	unsigned long lProcessId = 0;
	::GetWindowThreadProcessId(hWnd, &lProcessId);
	if ((wndData.lProcessId != lProcessId) || (::GetWindow(hWnd, GW_OWNER) != (HWND)0) || !::IsWindowVisible(hWnd))
	{
		return 1;
	}
	wndData.hWnd = hWnd;
	return 0;
}

HWND GetMainWindowHwnd(unsigned long lProcessId)
{
    ProcessWindowData wndData;
	wndData.hWnd = 0;
	wndData.lProcessId = lProcessId;
	::EnumWindows(EnumWindowCallback, (LPARAM)&wndData);
	return wndData.hWnd;
}