I had the same problem on my HP Elitebook 8350w running Windows 7 Enterprise. In Vista there was an HDMI output. In Windows 7 there is just the default "SoundMAX Integrated Digital HD Audio" speakers and SPDIF Interface. I had to switch the default output sound to SPDIF and it started working. Of course it has to be switched back to Speakers later when I want the sound to come through the laptop speakers.