How can I set up Macs with dynamic IP addresses to update a server with a static IP? I have several clients who have Airport Extremes and Macs at their houses. They all have dynamic IP address from their ISP. I want to have their Airport Extremes register their IP addresses with my server, which has a static IP. Does anyone have a guide to set this up?

For example, if my domain is xyzdomain.com I'd like to register clientA.xyzdomain.com on my server. 

I realize I need to host my own dynamic IP server, but I'm not having much luck finding instructions for OS X server (10.8).
You can try and host your own dynamic DNS service or you could use one of several online dynamic DNS companies. 

While I have not implemented it, this MacOSXhints article appears to be a fairly straightforward solution via a FreeDNS account:

http://hints.macworld.com/article.php?story=20110812232611102