also, windows updates can fail to install the update for a USB under certian conditions, check in the device manager, then bring up the properties for all the aspects of the USB parts and pieces, and look at each ITEM in the drivers section.
are they SP1 drivers? SP2 drivers?
i discovered this when looking at SP instalation logs, where it says , something like item is changed, and so therfore windows does not update that item. its minimally discussed anywhere, so i assume it is uncommon, but it might be worth checking, as MANY usb updates have been done by MS in XP to address things.