Windows 2000 Service Pack 4. I don't know if there is update on ms.com, but it's should be out soon. Or, if you can't wait, search 802.1x on ms.com; I remember there is a patch for it already.
Win2K doesn't provide 802.1x authentication natively, and you got it from the driver that comes with your wireless card. The KB is http://support.microsoft.com/default.aspx?scid=kb;en-us;313664 for the patch. Quote: CAUSE You cannot enable 802.1x authentication on computers running Windows 2000 because support for 802.1x is not provided by default in Windows 2000. Therefore, the associated user interface (the Authentication tab) does not appear in the Network Connection Properties dialog box.