“I have been told that I should use WPA ‘encryption keys’ to protect my wireless network.”
Encryption keys are not a good idea in a wireless hotspot situation for several reasons. Firstly, handing out an encryption to a client will add a big technical complication to that client as they try to join your network as they must know how to use it. Secondly, once you have handed out your encryption key to one person then it is essentially no longer a secret, anyone and everyone can now know what it is. Thirdly, even if you do keep an encryption key secret and everyone manages to connect to your network there is still no protection from each other as there is no inter-client isolation. So a hacker can still browse around the computers that are on the network.
This is a public service, it isn’t like a home or office environment where resources are shared. The job of the service is do connect a device to the Internet and isolate and secure from all others.
Check out Google for WEP hacking and how secure it is NOT. There are thousands of referring sites on how to hack such networks. One popular WEP hacking tool is Airsnort.