I have been scouring the web for some basic (i.e. 'noob') questions
about setting up LDAP for user authentication. I've chosen this NG
because the test platform is a variety of MS boxes. Here's the story:

I have been asked (to put it pleasantly) to come up with a way to use
LDAP to authenticate users seeking access to an existing web
application sadly written in ASP. The goal is that the users are
authenticated using their login and password that they use to access
the existing network, wherever the application is set up. There
doesn't need to be any sort of directory browsing or anything like
that, simply an existing-account authentication method via LDAP.

The test environment consists of an NT4 web/mail server that is also
the domain controller (on it's last leg; LDAP is known to fail on
startup), a Windows Server 2003 box serving files (go figure), and a
2000 server. There is also a Redhat box available if absolutely
necessary. All user information is stored on the NT4 machine. I have
looked all over the place for some answers to some pretty basic

1. I have gathered that Active Directory, ADSI, and LDAP are somehow
related, but I have not been able to find a byte of information that
tells me if any or all come preinstalled on anything, or if I need to
do something to install them. Needless to say, the broken links that
litter microsoft.com are no help.

2. How to set up the LDAP server. I see many samples of code using
LDAP that have some fun-looking connection strings abounding with DCs
and OUs. I have not found any documentation that tells me what the
parts are that make up the string and how I find or configure them.

Those are my two basic questions, after which point hopefully I will
at least know what I need to ask. Unfortunately the prospect of
server upgrades is probably not possible at this point. The
management is under the impression that if it works there's no reason
to install a new OS and have to set up the web server again with stuff
that is actually useful, such as PHP. Any help will be greatly
appreciated, I've got a ways to go on this project and any guidance
would be a huge help. Thanks.