There is a (very, very unofficial) port that I'm working on for Microsoft Windows. I'm doing this as a volunteer; this continues paid work I did for my employer a couple of years ago. The web page is at http://lucas.bergmans.us/hacks/openldap/. There is not much there now, but at the least I suggest that people interested in OpenLDAP for Microsoft Windows subscribe to the announcements mailing list. It has extremely low volume and will provide automatic notification of new releases and so on.

Of course, since this port is an unofficial, volunteer effort, please do not bother the OpenLDAP developers or my employer about the Windows port.