Windows: Reinstalling Widows is a pain even if you have backups, but most people don't consider backing up their wireless network settings before they reinstall. That's where the Wi-Fi Network Backup Manager comes in.
As its name implies, the app saves all of your saved Wi-Fi network names, passwords and keys into an XML file that you can back up with the rest of your data. When you're finished reinstalling Windows, reinstall Wi-Fi Network Backup Manager and import the XML file to restore all of the old networks and their passwords.
The app works just as well if you'd like to share your Wi-Fi config with another PC but don't want to write down SSIDs and keys. Wi-Fi Network Backup Manager is completely free.
Wi-Fi Network Backup Manager [Microsoft Blogs Italy]