SetPriorityClass Problem

[dspirit]

I'm trying to run a program in low priority mode, not my C++ program but some third-party programs like iTunes and etc.

Here's my sample code

int main()
{
	HWND hWnd = FindWindow(NULL, L"iTunes");
		if (hWnd == 0)
		{
			cout << "Process not found!" << endl;
		}
		else
		{
			cout << "Process Found!" << endl;
			DWORD pId;
			GetWindowThreadProcessId(hWnd, &pId);
			cout << "PID: " << pId << endl;
			HANDLE hProcess = hWnd;
			SetPriorityClass( hProcess ,BELOW_NORMAL_PRIORITY_CLASS);
		}
	cin.get();
	return 0;
}

but the process is still at normal priority.