Pls. check that your USB2.0 drivers are intact and not corrupted.
By default, Windows will use only USB1.1 until you install the USB2.0 drivers for it.
i know for a fact that usb 2.0 is already in windows xp sp2.
in my case, the solution to this problem has always been that an option in the bios needs changing. flick your way through the BIOS Setup until you find the USB options menu. in there you'll find options such as 'legacy usb support' and others relating to USB speeds. enable all the USB modes and if it comes up with a list of selectable options like USB - High Speed, Full Speed, you want to select 'Hi Speed'