Not sure if this clarifies things or not, as it refers only to FW800 (1394b)devices being slowed down to FW100 speed, and not to the FW400 (1394a) devices that many of us employ in an audio setting. Nevertheless, see: >>
If you have hotfix 885222 applied on a Windows XP SP2-based computer, and then you upgrade to Windows XP SP3, an installed 1394b FireWire device reverts from S400 speed to S100
Ray