The WEP encryption standard fell first in the war against wireless insecurity, discredited by simple hacks. Now, with the arrival of high-speed wireless technology in the form of 802.11n, it is WPA's turn to feel the chill of obsolescence.
The tough fact is that if you want to use ‘n' wireless technology at high speed on even a single client it will almost certainly be impossible to do so with anything other than the more advanced and secure WPA2/AES; WPA and TKIP is out of luck. Every wireless ‘n' adaptor we have seen mandates the use of WPA2 (or no encryption at all) in order to get the full speed boost, failing which the client will revert back to plain ‘g' levels of throughput.
Put in practical terms, to get even a single laptop to connect to an 802.11n access point at high throughput levels will require that every other laptop or remote PC use WPA2 as well, even if they are only configured with 802.11g adaptors capable of lower speeds. So the arrival of ‘n' wireless LANs forces a security upgrade if it is to be worth bothering with.
It is possible, by the way, that WLANs using WPA might appear to work with 802.11n products, but check the actual throughput levels you are getting. In most cases, it will be 54Mbit/s or, less often, and sometimes dedicated clients can erroneously report higher speeds which are not being achieved.
On Windows 7, Vista, and with any wireless product sold after about the middle of 2006, this won't be a problem, and it simply a matter of changing the client encryption scheme to match the wireless access point/router. But if your wireless card or PC dates from before that moment in time (which is to say most Windows XP machines) then an upgrade will be required.
Before fixing Windows itself, the first step is to check for new drivers for the PC's wireless adaptor after noting the version number of the driver itself in the properties tab in the XP wireless client. Anything before 2006 will probably need an update.
Actually finding these drivers can be a challenge because Windows sometimes can't find them using its own built-in driver update option. For instance, older but common Atheros chipset drivers can be very time-consuming to trace, and involved almost being hit with malware by criminals posing as a legitimate driver update site. Incredibly, the Atheros main site offered no drivers at all.
Once those are installed, check inside the Windows client to see whether WPA2 can actually be selected as a mode at all. If it can, the quest is at an end. If it can't, and the only encryption options are for WEP and WPA with TKIP, then Microsoft's official patch is needed. This can be found here.Next stop, usable Wi-Fi authentication.