Windows XP and Vista clients can get confused about EAP-Identity/Request
when they probe the network with EAPOL-Start. In such a case, they may
assume the network is using IEEE 802.1X and prompt user for a
certificate while the correct (non-WPS) behavior would be to ask for the
static WEP key. As a workaround, use Microsoft Provisioning IE to
advertise that legacy 802.1X is not supported.
This seems to make Windows ask for a static WEP key when adding a new
network, but at least Windows XP SP3 was still marking IEEE 802.1X
enabled for the network. Anyway, this is better than just leaving the
network configured with IEEE 802.1X and automatic WEP key distribution.