windows server - user authentication options

Hi

I'm trying to figure out my options for remote authentication for a
Windows server (terminal services access) out on a remote network. We
could go with local accounts, but that'll mean maintaining a separate
group of users.

I could setup a new active directory, but this would be outside our
current active directory on our local office network. Our security
policies restrict the active directory domain use to the local
network. So again, I'd have to maintain a separate group of users.

I do have access to a TACACS+ server (typically used for our remote
network element authentication), but I'm not sure how to get this
working with a Windows server.

Does anyone have a procedure for integrating Windows authentication to
TACACS+ or suggestions on how else to perform the remote
authentication.

Thanks for you time.