http://www.microsoft.com/athome/security/s...re/default.mspx
For those who are still using it, please update to version 1.1.1593 which is available for download here.
QUOTE
Microsoft Windows Defender is no longer installable or supported for Windows 2000....If you have version 1.1.1592.0, you must first manually uninstall Windows Defender before you can install this newer version...