After you update your computer to Microsoft Windows XP Service Pack 2 (SP2), the performance of your 1394a or 1394b FireWire devices may be greatly decreased.  Specifically, the issue can cause the bus speed to be reduced from 400 Mbps to 100 Mbps.  


Microsoft has published a fix within their online knowledge base.  To fix this problem, follow the instructions found at http://support.microsoft.com/kb/885222.