There's a couple of problem here I think.
You're likely to have a problem at your router. When a user requests a page from your server it will hit your router. The router, if it's doing it's job properly will act as a firewall and stop incoming requests. So to cure this, you need to forward one, some or all ports. Web page requests come in on port 80. So if you simply want to server up a web page, you need to forward port 80 on your router to port 80 on the local ip address of your server.... eg 192.168.0.100. However, if you're planning on hosting your own name server, mail server etc there are other ports you need to forward. You can set each one to forward individually or some routers allow you to forward ALL ports to one ip address.
Now, try typing the external ip address of your router into your browser. If the port forwarding worked you should get the apache 'It Works!' page.
If you only intend to host one site on your server then the easiest way to set the dns up would probably be to simply let go daddy deal with your dns. In the go daddy control panel set the name servers to theirs and from their control panel create an a record pointing to the ip of your router..... but I'd deal with the previous paragraph first.