As ian says go with WPA encryption if possible.
64bit/128bit Wired Equivalent Privacy (WEP) encryption has a problem, the wireless data is encrypted and decrypted using a key. When wireless network devices authenticate with the router, access point etc, the full key is sent unencrypted across the air, once authenticated encryption is enabled.
The problem being is that if someone is sat outside your house with a wireless enabled laptop and a packet snifing tool, he/she will be able to see the key as clear text, they will then be able to gain access to your network.
With 64bit/128bit Wireless Protected Access (WPA) it's a different story, WPA uses Temporal Key Integrity Protocol (TKIP) which is basically when a client is being authenticated the key is sent and hidden if many different packets. Making it extremely difficult for a hacker to obtain your encryption key.
One other technique to secure your wireless network is to use Media Access Control (MAC) address filtering, most routers and access points now support this feature. Never heard of a MAC address? Every Network Interface Card (NIC) or network device has a unique MAC address, it enables network hardware like routers to obtain the devices Internet Protocol (IP) address. Example MAC Address, 09:00:07:A9:B2:EB.
MAC address filtering works by creating a list of your network adapters MAC address' on the router or access point. When a computer tries to access your wireless network if it ain't on the list it ain't getting in!
So, with WPA and MAC address filtering, your clients will need a key and will need to be on the list.
There isn't a wireless or wired network anywhere that is completly secure, if somebody has the mind and the skills to get in then they will, eventually. But at the end of the day all home user's need to be worried about is if that thirteen kid next door can see my porn collection!
J