I am no DNS expert, but the domain ns1 and ns2 (named server settings), point your domain to the DNS Server. Within DNS, you need to setup the A record and such so it points to the web server (IP). If you are running your own DNS server, even if on the same machine, you need to make DNS entries that then point to the "web server IP", (IIS). Once IIS is configured properly to point to the DotNetNuke installation, the http alias record in DNN is the same domain as setup within IIS.
If you are going to have IIS point to the same DNN install with multiple address (aliases), each alias may be added in DNN also. Another purpose of the alias in DNN is to distinguish between sites. If you have multiple portals on the one install of DNN, IIS may point to the install with multiple address or even multiple domains, at least one for each portal. Once a request passes through DNS, and through IIS, to the site, DNN determines which portal to bring up based on the aliases set on the portals. So, if you have two portals on one install, the "website" within IIS could be set up with both addresses. In DNN one portal is set with one address (http alias), and the other portal with the second address (http alias). DNN separates the two for you, based on the alias record.
If you are unable to bring up the portal with the domain name, I would suggest you first work out DNS by trying to bring up a basic html site (page). If you can't bring up a basic page, something is wrong with your DNS entries or IIS. There are some nice tools to help you check DNS settings at http://dnsstuff.com/ If you can bring up an html page with the domain, then DNS should be ok, and you can then focus on IIS configuration for Asp.net.
Hope that helps a little