Do you see a chance to integrate/link Windows Environments and/or LDAP via OpenSource Penrose - a java-based virtual directory server?
http://v1.safehaus.org:8080/display/PENROSE/Home
They lack a Mac OS X version. I did not try to compile the source yet, though.
Should be worth a try to make a connector.

How do you see the integration to work. Address Book Server already supports LDIF exports and scripted automation via wget. Bi-directional integration is unfortunately not possible due to limitation on LDAP and the lack of a standardised ldap schema.