remove exchage 2k

i’m trying to uninstall exchage server from my win 2k server ( i only have on eserver)
and i get this error:
the componenet “ms exchaneg and clobration services” can not be asssigned the action remove:
becouse
one or more users currently use a mail box store on this server this usesr most be moved to a mailbox store on a diffrent server orbe mail disabled before uninstalling this server.
unforunatly i only have one server.
what can i do to uninstall this server