I have to apologize-- I confused two issues. What I recommended in my post above had to do with MAC device filtering, not WEP.

While it's true that XP per se does not store the WEP key, you *can* install connection managers that will do so. The tablets have one built in. On my laptop, I use a tool provided by Intel, called Intel PROset for Wireless (it came with my T43). You should be able to find such a management tool for your device was well, probably provided by the Wifi chipset vendor.