
The graphics driver is the driver for HDMI audio, not the regular audio driver. If there is still no option to select "HDMI' as the default audio playback device, try re-installing or updating the graphics driver, or even try an older version.

XP does not have "show disconnected devices". If "HDMI" is not there, right click in the white area and look under "Show Disconnected Devices" or "Show Disabled Devices" and see if it is there.

Turn off the computer and projector before connecting the HDMI cable.On models with Intel graphics the HDMI audio driver will appear in the Device Manager as "Audio Device on High Definition Audio Bus" or "Intel Display Audio". HDMI audio is incorporated into the graphics card's driver so make sure you have the newest version of your graphics card driver. HDMI has its own audio driver separate from the audio driver.Later, after you get your HDMI audio working, if you find that it still does not work on batteries you can change your power management settings in the Control Panel.

Some of the models have a power management scheme that will not allow for HDMI audio while running on batteries.
