no idea, i mean as far as the demo goes everything works fine for me sound included. there were some threads about having to remove hid in device manager to get it to work but i think for them its just running the game, not the sound problem
do you have a creative soundcard? if so you might need to update alchemy drivers/addon
if not i have no clue, other then what people said about removing hid stuff from device manager. some guy said he ha to remove his dialup modem which is weird so no idea.
also is your dx9 updated?