You can use DevCon command line to remove all devices related to USB thumb drives.
That command line should be able to dig into the registry, remove any traces to the USB drive, essentially forcing Windows Xp to install the drivers for the USB thumb device again.
Plug in your USB thumb drive
Open up command line and type in the following command (making sure the CMD can find DevCon.exe)
devcon.exe find usb\*
It should list a number of USB devices. Watch out for USB Mass Storage Device
To the left, there is a string of serial number, i.e. USB\VID_0781&PID_5151\SNDK2FCA65161B809607 (it should be different on your machine)
Copy the string
Next, issue the following command
devcon.exe remove <insert the string here>
Remove the USB thumb device.. Reinsert it again. Windows Xp should tell you that it discovered "new" device, aka the USB thumb device.