You can do an initial synchronization via LDIF, LDAP Data Interchange Format. Do an LDIF dump from your LDAP-Server database and import the records into Active Directory using the LDIFDE tool that ships with W2K.
Once you've populated Active Directory, you can modify your web tool to update both Active Directory and LDAP-Server at the same time.
If you have a large database with many administrators, you might want to look at a metadirectory service such as Netscape Metadirectory Services or Microsoft Metadirectory Services. Be prepared for a long and tough installations but the end result is a tool that can fully manage both databases.
Personally, I think you'd be better off doing your own coding. You sound as if you have enough experience with LDAP programming to build the tools you need.
This was first published in May 2001