Windows XP and Windows Vista do not require additional device drivers and the Microsoft device driver should install automatically when the USB Flash drive is plugged in. However, some computers, especially laptops, may not provide enough stable electrical power to all or some of the USB ports to allow the USB Flash drive to function correctly. This is a more common problem with larger capacity drives (over 4GB) and sometimes even on desktop computers with front panel USB ports.
If you're using the USB Flash drive in the front ports of a desktop computer, try attaching the drive to the USB ports in the back. Sometimes the rear ports have a higher power budget. Also try connecting the drive through a powered USB hub. By using a powered hub, the computer doesn't have to provide the power. If the USB Flash drive works through a powered hub, but not when connected directly to a USB port on the computer, the problem is almost definitely caused by insufficient power. There is nothing that can be done to reliably correct the problem if it is caused by power.