Hello
DidI understand You correctly:
You have a static ( non dynamic ip) but want to use adynamic name e.g.
www.dyndns.org ( free service) or
www.dyndns.com (commercial)
Next: make sure you have a public ip: your ISP is not blocking any ports.
Go to the page were you register your domain, what you want.
1st possible solution:
when installing the server( dont remember about configuring;) haven't done it quite a while) it asks for a domain name you type in what you registered. example: you.dyndns.org the next step is it asks if you want to use a dynamic dns, if you registered in one of those listed in setup, select it.. so even if your ip should change for a wierd reason, the name points still to your server.
finish setup and you are done

2nd solution: using virtual doamins in server manager
go to your servers server-manager open the virtual domains panel and there add a new virtual domain. configure it, save it and that should be it.
hope this helps
sander