There are any number of good books and resources available for you to learn about Active Directory and other Microsoft technologies. Perhaps the best thing you can do is to install a test server for yourself and start trying different things to see what happens -- you can download a trial version of the Windows Server 2003 software from the Microsoft website. I would also recommend subscribing to the ActiveDir list-serv, hosted at ActiveDir.org, where you will find wit and wisdom from many Active Directory experts. You'll also find a lot of useful information on the Microsoft website itself; there are entire sub-sections of the site dedicated to different technologies including AD, DNS, and other networking and directory technologies.
This was first published in August 2006