display window transparent

[netrobot]

vc6

SetWindowLong(this->GetSafeHwnd(),GWL_EXSTYLE,
	GetWindowLong(this->GetSafeHwnd(),GWL_EXSTYLE)^0x80000);
	HINSTANCE hInst = LoadLibrary("User32.DLL"); 
	if(hInst) 
	{ 
		typedef BOOL (WINAPI *MYFUNC)(HWND,COLORREF,BYTE,DWORD); 
		MYFUNC fun= NULL;
		fun=(MYFUNC)GetProcAddress(hInst, "SetLayeredWindowAttributes");
		HWND appwindow = this->GetSafeHwnd();

		if(fun)
		{
			StbcvSim(appwindow,0,0x50,2); 
		}
		FreeLibrary(hInst); 
	}

dann ist die gesammte app transparent, was ich will ist nur display window transparent, wie mache ich das?