I'm not sure about what your doing, but here's some of what I have learned using easydns.com which I highly recommend
First, (you probably already know this) but it can take up to a few days for the dns settings to filter out over the net.
Second, some cable companies will block port 80, so you need to use a different port if your hosting the site youself.
Third, You should be able to read the external (public ip) from the setup utility for the router. I use a linksys router and a toshiba cable modem) The linksys web based setup utility will show me the currently assigned IP from the cable company. I have 2 netcams internally that I assign static (private IPs) using different ports (not ones blocked by my cable company). using easydns I forward differnt domain names to 22.214.171.124:101 for example (126.96.36.199 being the IP handed to me from the cable company and 101 being the port). This works great since easydns has a "stealth" feature and the user only sees something like Name1.cameltoejoe.com in their address bar.
There are public and private IPs. The private ones are typically what you use on the inside of your router. These addresses are used by many people, but will not route over the internet. I'm certainly no expert, but if this is helpful, I can ramble more.
PS:Easydns is cheap, and I get like 100 email addresses that can be forwarded to any other email address and I think like 100 web addresses that can be forwarded to different servers.