Practicallynetworked.com offers several steps to protecting your wireless network from hackers.
Don't use TCP/IP for File and Printer sharing!
"Access Points are usually installed on your LAN, behind any router or firewall you may be using. If someone successfully connects to your Access Point, they’ll be on your LAN, just like any of your other clients. But since they’ll be using TCP/IP to make the connection, you can easily deny access to MS File and Printer sharing by using a protocol other than TCP/IP for those services. That way, they may get access to your Internet connection, but they won’t get access to your files!"
Follow secure file-sharing practices
"Share only what you need to share (think Folders, not entire hard drives), and password-protect anything that is shared with a strong password."
Use WEP Encryption
"A weak lock is better than no lock at all, so enable WEP encryption and use a non-obvious encryption key."
Secure your wireless router
Your router should require a password to access its administrative features. Change your password from the default and use a complex one (numbers and letters).
Use VPN
If you don't want to take chances with your data, run a virtual private network tunnel over your wireless connection, too.
For more information, visit www.practicallynetworked.com.