Plug your USB flash drive into an active USB port on your computer.
Open the My Computer (XP) or Computer (Vista) menu from the Start button.
Find your USB drive in the list of drives in the Computer/My Computer menu. The drive letter will vary based on your system configuration.
Right-click on the drive listing and choose "Format" from the pop-up menu. The Format Removable Disk dialog box should appear.
Click "Start" in the Format Removable Disk dialog box. Windows will complete the format and alert you when it is finished.