When you connect to Wi-Fi networks that use a static encryption key or passphrase, such as WEP and WPA/WPA2-PSK, it is saved by Windows. This way you don’t have to type the key or passphrase each time you connect.
If you forget the network key, you can use a utility to recover it from Windows. WirelessKeyView from NirSoft is one example. Simply download and run the utility. You’ll see the encryption keys appear for each wireless network profile in Windows.
Keep in mind, Windows XP automatically converts WPA passphrases into a new binary key that contains 64 hexadecimal digits. However, you can use this key just like the original one when connecting to the Wi-Fi network.
Remember, anyone that can get ahold of your computer can also do this. This is why it’s better to use the Enterprise mode of WPA or WPA2, which uses 802.1X authentication.