i had the same situation with my macbook black.
i tried manytimes uninstalling and reinstalling the audio driver using the files on my macbook DVD... but doesn't work.
so I tried to download the new version of the driver... it says compatible with windows 7 and finally it works! my soundcard is Realtek... here is the link
ftp://202.134.71.21/pc/audio/VistaWin7R242.zip
if ur mac uses SigmaTel then perhaps downloading the new SigmaTel driver will solve the problem...
cheers
Message was edited by: mbblack.......................