The screen lock is available on the iPod Touch, as well as recent models of the iPod, and iPod nano, allowing you to set a 4-digit passcode to lock the screen. This is to prevent others from using your iPod, but it is not an impregnable security device. If you forget the passcode, you can quickly and simply unlock the iPod by connecting it to the computer you normally use to sync your iPod with iTunes. You can then open the iPod and reset the lock to a more memorable passcode.
Connect the iPod Touch to your computer using the USB cable.
Wait for iTunes to open and sync with your computer.
Eject your iPod Touch from the computer by clicking the "Eject" icon beside the iPod's entry in the "Devices" section of iTunes.
Disconnect your iPod Touch from the USB cable. Your iPod Touch will be turned on and will be unlocked.
Tap the "General" menu on the iPod Touch. Tap "Passcode Lock," and then tap either "Turn Passcode Off" or "Change Passcode." If you tap "Change Passcode," you can then enter a new passcode.