well, first you have to register a domain and have it automatically forward to yourusername.no-ip.com if you don’t have a static ip address. All no-ip.com lets you do with your free account is forward it to a dynamic ip and then you run their app on your server and it automatically checks your ip address every thirty seconds or so.
Then you also have to open up the ports on your router, it depends on if you have cable or dsl really. Usually cable will block traffic on port 80 because everybody uses the same line and they don’t want to get tons of traffic that they aren’t getting payed for. DSL generally lets you because you have your own line. If you have a linksys router, just set up the dmz host to the private ip (192.168.1.xxx) of the server.