If you have an AirPort/AirPort Extreme or Express Base Station do the following:
1. Launch the AirPort Admin Utility located in the Utilities folder (Applications/Utilities)
2. Click on your AirPort name and then click Configure.
3. Enter your password (if you have one which you better!)
4. Under AirPort Network you will see the name of it, and then just under it is a checkbox that says Create a Closed Network. Check that box and the AirPort will not broadcast your AirPort Name.
You may also want to change your AirPort name since your neighbor knows it now.
Another thing I would do is I would enable MAC Address Filtering. You can also do that while you're in the AirPort Admin Utility. Basically you can do this by clicking on the Access Control Tab and then Click the + on the right side of the box and enter in ALL of the MAC Addresses of the Macs/PCs that connect to your network in the house. You can get the MAC Address of the wireless card of any Mac by going to the Apple Menu and then click on System Preferences. Then click on Network and select AirPort. The AirPort ID is your MAC Address for the wireless card.
FYI: MAC Address has nothing to do with the Mac computer.
When you're finished making your changes inside the AirPort Admin Utility, click the Update button in the lower left. Click the Ok button the next screen and the AirPort will restart. It will take a few seconds for the AirPort Base Station to restart.
