I only recently bothered to look up this issue I have had since 2007, only since I am about to buy an external HDD.
So I custom built the system a while ago and XP SP2 never auto updated my USB 1.0 driver to USB 2.0 (hence problem).
It is pretty straight forward to fix this with all the information on the Microsoft support site, but I thought I would add it to UGN as well:
To resolve this problem, install Windows XP SP2, and then update the drivers for the USB devices that are connected to your computer. To update these drivers, follow these steps:
1. Click Start, click Run, type devmgmt.msc, and then click OK.
2. Double-click the type of device that you want to update.
3. Double-click the specific device that you want to update.
4. Click the Driver tab, and then click Update Driver.
5. Follow the instructions in the Hardware Update Wizard.
6. Repeat steps 2 through 5 for each USB device.
Note You can also install Windows XP SP2, and then disconnect and reconnect the USB devices that are connected to your computer. By doing this, you start the Plug and Play utility. The Plug and Play utility updates the version numbers for the drivers.
I should have done this ages ago. I now have 10 USB 2.0 slots available. I only use 5. An extra 4 came from buying a USB 2.0 card thinking my P5N32-E SLI plus Mobo didn't come with any lol.
Oh and the Mobo driver support disc came with a USB 2.0 driver but it detected XP SP2 and would not update.