<< the host is where your files are at. it hold an ip address. when you register your domain you tell it the ip address of your host. then whenever anyone calls your domain, the servers route them to your host. you can change names no problem, you just tell it the ip and change/cancel it from the previous one. >>
Not quite right... When you register a domain, you register the primary and at least 1 secondary nameserver that will handle the name resolution for the domain. Not the IP of the host. When you type the name into a browser, the browser will query the named server in your IP settings for the IP address, if it does not know it (not in cache), it will query the root nameservers for the nameserver that handles the domain. It will then ask THAT server(s) for the IP address to connect to.
If you changed hosts, the root servers don't necessarily need to be changed. The "authoritative" nameserver does. If the nameservers change the root servers will have to be updated.
To change names file the new name with a registrar, and then ask the hosting company to add it to the nameserver, and remove the old one. The web server will also likely need to be updated, because at the prices we're talking here you won't be getting an IP address to yourself - you'll share it with others. Which means the web server (httpd - probably apache) will need to know about the name switch as well to serve up the correct files. How can you tell if you have a unique IP or a shared, easy type the IP address into the URL box on your browser. Does your page come up? It's probably a unique IP. If something else comes up - it's a shared IP system.