Maybe your USB drivers need to be updated . It should just be plug and play the drivers for a USB keyboard are included in WindowsXP . If the keyboard came with a CD install the software for it ? You also can try the System File Checker > start run type "sfc /scannow" without quotation marks and note the space between the c / mak sure you type it exactly that way . You will be prompted to put the WindowsXP installation CD in eithe your retail or OEM version should be fine. If you have auto play enabled on your CD/DDVD drive just keep tapping the shift key untill the light on the drive CD drive stops blinking from it trrying to access the CD . Once that stops continue the System File Checker utility !
Good Luck ,Nick
Always set a restore point before you perform any action that may alter your file system ,System File Checker scans your system replacing any missing system files !