It's been a few months but we reloaded a machine at the office with "XP" and sure enough it could not connect to our WPA2 protected WiFi. It took updating to the latest service packs and more then a driver update from the laptop's maker to enable WPA2 WiFi access.
Your post noted "XP" so as presented it should have problems on many networks.
It's a shame details are slim. Some older laptops are well known to have WiFi issues and you find discussions about cleaning with canned air, reseating or replacing the WiFi card. But we can't have that discussion as the make, model is missing.
I have Acer netbook (Windows XP) and from last few days, connection to internet is real challange. I can see wireless network availability but when I tried to connect, it was not connecting at all. Sometimes there is warning message popped up at task bar "unable to connect preferred network". I tried to change wireless network setting but no help. Is there any known issue? I also checked services but can;t figure it out what goes wrong.