From Wi-Fi Networking News: A short, to-the-point article on sets out a handy list of the basic rules for making a solid effort to secure a wireless home network.
To summarize:
1. Change the System ID
2. Disable Identifier Broadcasting
3. Enable Encryption
4. Restrict Unnecessary Traffic
5. Change the Default Administrator Password
6. Patch and Protect Your PCs
If you want to play wireless networking, consider these six steps to be the minimum price of admission. Anything less is irresponsible.