When Microsoft released Service Pack 2 (SP2) for XP, they inadvertently introduced a speed downgrade for 1394b to S100 from 1394a S400 and 1394b S800 capability, as referenced in http://support.microsoft.com/default.aspx?scid=kb;en-us;885222.  Then with XP SP3 the problem persists, and in Windows Vista as well.  Finally resolved in Windows 7.

For users of AVT's FirePackage this is irrelevant, as FirePackage uses the Intek driver, with robust, determinstic high-speed S800 capability.

XP SP2 and SP3 workaround:  For users of AVT's Active_FirePackage, the CMU driver, National Instruments, or Cognex users, please either follow the notes in the Microsoft document linked above, or for a more user-friendly approach simply download and run this driver rollback utility. 

Vista users (also fine for XP SP2 and SP3): Please use the AVT 1394 Bus Driver Package.