If you are experiencing problems getting a WiFi card configured to use WPA where WPA support is via a supplicant then I hope this post might save you the hours I wasted trying to get it working.
You will need to download a WPA supplicant. If you are using D-Link equipment you can get the supplicant from the D-Link website or you can purchase one from a couple of software houses.
You will also need WPA support in Windows. If after you install the supplicant and you go to the Wireless Network Configuration dialog (check the 'Use windows to configure my wireless network settings' box first) and on the Wireless Networks tab you see options for WPA then there is nothing more to install and you can configure WPA and away you go.
If on the other hand there are no WPA settings on that page then you will need to install a Microsoft patch to add WPA support to Windows. If you are using Win XP sp2 then download Q815485_WXP_SP2_x86_ENU.exe from Microsoft and install that. I think there is a patch for Win 2k but you will need to check. You should now see WPA support in the Wireless Networks tab.
Hope this helps someone...