No. Search here for "ldap authentication" and "Active Directory" and you will find many similar questions and answers.
CharlieBrady, I don't see how Active Directory will solve this problem. I'm looking for the same type of setup, and if I wanted to run Active Directory, then I most certainly won't look @ linux, or SME for that matter. Linux SME is supposed to be a OSS replacement for MS products. Have you ever considered that there may be users who would need some sort of replication between user accounts on more than one SME server? This has a LOT of advantages.
Doing a search for "ldap authentication" returns only this thread. Would "ldap authentication" solve this problem? If so, how?