http://support.microsoft.com/kb/885222
sorts a speed problem that some people are encountering when sp2 is installed. 
Just to provide a bit more detail.
Below is an extract from the download page that explains who might need it and why.
Seemingly, it's required only if your PC has fast FireWire 1394b ports and you have installed the SP2 updater for Windows XP.
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SYMPTOMS
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. A digital camera that uses S400 speed is an example of such a device.
CAUSE
This problem occurs if you connect a 1394a or 1394b FireWire device to a 1394b port. This problem occurs because Windows XP SP2 changes 1394b ports to S100 speed when you upgrade.
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Bob C
As a little update - I've discovered that this fix won't work on my Athlon 64 3200+ system, which is centered on a Gigabyte GA-K8VNXP motherboard with 1394b and 1394b.
Says something about can't complete because a file exists.
:(
Bob C