You can administer AirPort Express from Mac OS X, Windows XP, and Windows 2000. The AirPort Express Assistant provides an easy way to set up AirPort Express, but it's specifically designed to be compatible with Mac OS X or Windows XP. To set up AirPort Express from a Windows 2000 computer, you must use AirPort Admin Utility for Windows, version 4.0 or later.
The AirPort Installer does not install AirPort Express Assistant on Windows 2000 computers, and you shouldn't copy it from a Windows XP computer.