If you're not sure if your hardware and software supports WPA2 Personal, use WPA Personal.

2. From the Encryption Algorithms drop-down list, choose TKIP. In the Personal Key box, type a key between 8 and 63 characters in length. The longer it is and the more random the characters, the more secure it will be. Write down the key. You'll need to use this on each wireless PC on your network.

3. Leave the Group Key Renewal row at 3600. Click Save Settings. That applies the key to your network. Now, only PCs that use WPA encryption and the key you just generated will be able to get onto your network.

Next, configure each wireless computer on your network to use WPA and the key you just generated. (Wired PCs don't need to be configured.)

For each Windows XP PC:

1. Click the wireless connection icon in the system tray, then click Properties, click the Wireless Network tab, highlight your network, click Properties, and then click the Association tab.

2. In the Network Authentication drop-down box, select WPA-PSK. In the Data Encryption dialog box, choose TKIP.

3. When you do that, the box that reads "The key is provided for me automatically" is checked. Uncheck this box. Enter your WPA key in the "Network key" box, and type it again in the "Confirm network key" box.

4. Click OK and then OK again. Now the Windows XP PC can connect to your network using WPA encryption.

In Windows Vista:

1. Select Control Panel --> Network and Internet --> Network and Sharing Center --> View Status.

2. From the Security type drop-down box, select WPA-Personal or WPA2-Personal, depending on your encryption method.

3. From the Encryption type drop-down box, select TKIP. In the Network security key box, type in the security key you used on your router.

4. Click OK. Your Windows Vista PC can now connect using encryption.

If you've got a small or medium-size business, and are looking to encrypt your network, you might consider an outsourced solution, such as SecureMyWiFi from WiTopia. Prices for SecureMyWiFi vary according to your network size, and start at $99 per year for one wireless access point with 100 users.

Protect yourself using MAC addresses

There's another way to protect your wireless network: Tell it to allow only certain computers to connect, and ban all others. To do that, you'll filter by Media Access Control (MAC) addresses, which are in essence IDs for wireless adapters. Every piece of networking hardware has a unique MAC address. So you'll be able to tell your router to allow only specific MAC addresses onto the network and keep all others off.