Could you talk us through exactly what you did.
1. Did you reinstall XP or did you do an upgrade from a previous version of Windows?
2. Were the USB 2.0 ports working prior to the install/reinstall?
3. How do you know that it is the ports that are not working? Could it be the equipment attached to the ports that is not working? Could it be a faulty cable? Have you installed the correct drivers for the equipment?
4. What is Windows Device Manager reporting? When you interogate the USB ports in WDM is it reporting everything OK or that there is a problem?
5. Have you run the Windows "Troubleshooter" on the ports?