The main information required to configure the existing wireless network is the wireless network key (it's a kind of password). Now follow the steps discussed below-
1. Click on the Start button and click the left mouse-button.
2. Inside the push-up menu, move the mouse-pointer and place over the Control Panel option.
3. Open the Network Connections
4. Choose the Properties by right clicking the Wireless Network Connection.
5. Select the Wireless Network tab.
6. Now you can select one of the options from the following:
a. Set up a new wireless network
b. Add new computer or devices to the test network (test wireless connection already exist).

Windows XP automatically performs for you the following:

• Informs you when new wireless network gets available
• It will automatically configure the wireless adapter required.
• Attempts to connect.

7. If you choose the existing wireless network setting, again you have to specify whether to connect through an existing access point or to connect to an existing computer.

8. If you have selected the option to connect with an existing access point, choose Configure and in the wireless Network properties dialog box, specify the network key settings, or choose that key is automatically provided for me.

9. If you have selected to connect through an existing computer, select the network name under Available Networks and choose Configure. Again specify the network key in the wireless Network Properties dialog box or alternatively you can select that the Key is to be provided automatically.

10. If the access point and computer are in the range of your computer, choose the Advanced button, and then select Computer-To-Computer (Ad Hoc) Networks Only.

11. Apply the settings and close the window.