As for other servers, I just looked at http://verzeichnisdienst.de/ldap/Server/ and saw some interesting stuff : eudora and ibm both provide freeware LDAP-servers for NT/2000.

IBM uses DB2 as it's backend, which has an awkward licence attached to it.
Eudora is a port of openldap to win32. It uses DB files as backend. I've got it running on my win2k box.
Anyone can try it using:

ldapsearch -h fvgestel.dyndns.org -b o=empegcar cn=*

Frank van Gestel