Did WinXP confirm that you connected to the wireless network you found?
-- If so, check your IP address and the status of the connection - number of packets sent and received. It is possible that XP is automatically assigning an incorrect IP address. You can try disabling the network connection and then re-enabling it to see if it assigns a working IP adress.
-- If not, the wireless network may have security enabled that would require you to enter the correct password to make the connection.