Did you download the driver from Asus?
http://support.asus.com/download/download.aspx?SLanguage=en-us
Just cut and paste this below into the
Input Model to Search in the upper left corner and press Enter:
M2n32-SLi Premium Vista Edition
Then select it (in the top middle) to see the list of drivers. Scroll through the list and you will see the audio ones.
Shawn