After struggling to find WPA2 drivers for the Microsoft Wireless PCMCIA adaptor (MN-520) for a newly rebuilt laptop, I decided to post instructions as to where to find them. Especially, since this product has been discontinued by Microsoft and for some obscure reason removed them from Windows Update.
Anyway, to install the drivers you need to install original Microsoft Broadband Networking Software from Microsoft, and then the updated version with WPA2 support. As a third step, you also need the WPA2 update for Microsoft Windows XP (you do need a genuine copy of Windows for step 3).