well, from your posts above i've been reading your audio device (on the mac pro) is the mbox2 and google returns a lot of results with asio problems on vista, so i asked for firmware and driver version ....
guitar rig is a software, right? so which ASIO (from which sound device) do you see in rig kontrol?
christian
and remember: only a CRAY can run an endless loop in just three seconds.