Though they can be bought for less.
Ebuyer USB 2.0 4 Port PCI card £7.04
http://www.ebuyer.com/customer/produ...duct_uid=32620
4 Port USB 2.0 PCI Card - 3 External & 1 Internal
£7.99 inc VAT (£6.80 ex VAT)
24 in stock now
http://www.dabs.com/uk/Search2/Produ...rase=usb%20pci
Plugging this sort of thing into a PC with Windows XP installed is not something you should worry about, the OS is 98% likely to find and configure the new card without you needing to do much more than stick the Windows, or supplied CD into the machine.