Most manufacturers’  Wireless utility programs support WEP but not WPA.

You should instead use the wireless functionality built into Windows XP with Service Pack 2.  From the Wireless Network Connection Properties, tick the box for “Use Windows to configure my wireless network settings”.

Then select your wireless network in the “Preferred Networks” section and click the [Properties] button (or click the [Add] button if your network is not listed).  Choose Network Authentication “WPA-PSK” and enter the pre-shared key into the “Network Key” field.

You will of course have to enable WPA and enter the same pre-shared key into your wireless access point or router.