Active Directory is not a software component per se. It's a component of an operating system. Just like Windows 7 and Windows 8, there is Server 2008 and Server 2012. You would essentially replace Windows 7/Windows 8 with something like SBS 2011 Essentials (if you are still on AC 6.3) or Server 2012R2 Essentials. You can then join existing desktops to the domain/active directory. I did a video series on this for SBS 2011 Essentials.
Of course, you get tons of extras like Server Health Reports, Network health reports, backups of all desktops, Remote Web Access, and much more. It really streamlines things for a practice.
.png "ACUF Donor I")
