I got this from HIS's website
(If the images aren't showing up, right click the broken images below and copy the url, then paste them into another tab):
Windows Vista / Windows 7 Users:
Go to Control Panel (select classic view in the top left if needed)
Now find sound and click on it.
You should now see a list of playback devices, select Digital Output Device (HDMI) and right click on it. (depending on your HIS graphics cards and it could be slightly different)
On the right click menu select Set as Default Device.
That’s it, simple as that! The audio controller on your HIS graphics card will be the default sound device.
You might have to select the volume control in to the system tray and ensure the volume is fully turned up.
Your sound will now be going through the HDMI cable to your TV or Receiver as well as the picture.
If you ever want your sound to play though your computers sound card just set it as the default device again.