SBS, Small Business Server?
You will need to setup a default document, on your server, something for your server to use. Then sort out your Internet, is Port 80 alowed? Then if you have a router then you need to route port 80 to your server.
Once thats all finnished, create an A-Record in your DNS settings. To point to your routers IP address then hey-presto, type in 'server.yourdomain.com' and it will load up the page on your server.
It sounds like your trying to use Active Directory, I woudn't unless you really need to. Its really hard to setup.
Hope I helped, I'm usualy online so add me to one of my IM address's if you like.
Nick