Information about this driver can be found here:

http://support.microsoft.com/kb/888111

The driver download is here:

Microsoft* High Definition Audio Package (must install XP SP2 first, then kb888111.exe, and then the audio driver).

http://downloadcenter.intel.com/confirm.aspx?httpDown=http://downloadmirror.intel.com/11036/eng/kb888111.exe&agr=&ProductID=954&DwnldId=11036&strOSs=&OSFullName=&lang=eng

In systems that use UAA, this driver should be installed *before* any other audio drivers.