Do you have any firewall software installed or the windows xp firewall enabled? If so this could be your problem. Also you might try changing the channel on the ap as there might be interferance on that channel and it the computer is more suseptable than the access point. Also is wep enabled on the access point and are you getting an ip address from the access point? You might also see if there is an update to the drivers as well. Are you using the windows xp wireless config or the one provided with the nic?