Switch Audio Output Device Automatically Between HDMI And Speakers

I have a laptop (Dell XPS M1330) running Vista Home Premium 32bit featuring an HDMI port and, as far as I can see, a soundcard called SigmaTel High Definition Audio. I regularly watch videos on my LCD TV using HDMI and I am constantly annoyed by the fact that the audio output doesn't automatically switch over to HDMI when the cable is connected (or vice versa when the cable is disconnected).

One would expect it to do so as this is how it generally works when f.ex. headphones are connected and indeed, on my laptop, the audio switches from speakers to headphones automatically without any problems. My solution to the problem is to manually change the default output device to HDMI and then restarting the media player. I cannot see why this operation cannot be automatic, and therefore I ask of you all if there is any way to accomplish an automatic switch from speakers to HDMI when an HDMI cable is connected