I have recently installed a new USB 3.0 PCI Express card into a windows XP machine with USB 3.0 and eSATA ports. I am running service pack 3 and have updated the firmware and drivers for the Renases USB 3.0.
The USB 3.0 doesn't show the buffalo drive in my computer or disk management, but it does show up in device manager and in the safely remove hardware window.
The buffalo drive does show up while using USB 2.0 cord or an eSATA cord.
XP does not officially support USB 3.0, you need Windows 7 for that. At this point there will not be any official fix to hack in USB 3.0 support into XP, so your options are to try and find an unofficial fix, or to upgrade your operating system.