USB drivers are installed automatically anytime a USB port is enabled in bios setup. Drivers are provided automatically by the operating system. SP1 or SP2 must be installed in order to get USB 2.0 support.
btw, usb drivers are written to the hard drive (by default) during installation of the os. They are hidden within the file driver.cab at this location:
And the USB drivers are also on the installation disk in the same driver.cab file.