Say that your computer (running Windows XP) is connected to internet via LAN and you wanted to share the connection to other devices via WiFi.

1. Go to Control Panel > `Network Connections.

2. Right-click on the Local Area Connection and choose Properties.

3. In the Advanced Tab under the Internet Connection Sharing, enable Allow other users to connect through this computer's internet connection.

The next part is to create an ad-hoc Wi-Fi connection. My netbook comes with an Atheros wireless network adapter. So I am using Atheros Client Utility to configure wireless connections. You may use Windows XP's default tool as well.

1. Open Atheros Client Utility.

2. Under Profile Management tab, click New.

3. Fill in the profile name and give an name for identifying the Wi-Fi connection under the SSID1.

4. In the Advanced tab, change network type to Ad-Hoc.

5. In the Security tab, choose Pre-Shared Key (Static WEP) and click Configure.

6. In the popup menu, choose ASCII Text for Key Entry and give a password in the Encryption Keys section for WEP Key 1 (one would be enough). Depending on the chosen WEP Key Size, the length of the key varies.

7. Click Ok and finish the configurations.

8. Back in the Profile Management, choose the currently created profile and click Activate.

Now you can connect to the internet via the newly created Ad-Hoc Wi-Fi connection. To connecting to the network, you need to enter the same password given for the WEP key in step 6 above.