Check to make sure your Windows XP machine has the latest updates (including Service Packs) installed from Microsoft. Open Internet Explorer on the Windows XP machine to http://update.microsoft.com/ and install any updates seen when you perform an Express check for updates. If there is a warning about a service pack being available (Service Pack 2, if you really have not been getting updates, or Service Pack 3 which was released two years ago), install the Service Pack and then install any additional updates seen after the reboot. Reboots will be common, and expect to visit Windows Update a few times until it all empties out. Microsoft released an update in 2005 adding WPA2 support to Windows XP, so it will be included in Service Pack 2, and for sure, Service Pack 3 of Windows XP.
Failing the availability of any updates, provide us the name and model of your wireless card. Also, using the Device Manager (Right click Computer, go to Properties, select the Hardware Tab, click Device Manager), open up the Network Adapters section and locate your Wireless card from the list. Double click on the device, and open up the Driver tab on the window that appears. Give us the Driver version and date for the card.
