Sounds like you need to read a bit more about the net and the web before doing this... I'll have a go at explaining though.
Originally posted by: SoundTheSurrender
So if I forwarded port 80 on my server how does the internet know that it's a server?
The internet doesn't 'know' anything - its just a collection of computers, it is not centralised in any way. The only difference between a computer which is a server, and one which is not a server, is what programs it is running.
When you type an address (IP or URL) into Firefox or IE it asks the computer on the other end if it is running a web server program on port 80. If it is, the server will then return index.html (or whatever) to the client, and that page will be rendered in the browser. If not, it will reject the request.
For example when I went into DMZ mode, I found out the IP address via ipconfig and asked my friend to type that IP in and it got pointed to my website.
Yep - even if you weren't using DMZ or running a server of any kind your IP would still point to you.
Basically your router is running something called NAT (look it up) which means it is the only computer on your network which can directly be seen from the outside. It is the edge or border of your little network. Anything which want to go to your server has to get through the router first.
I thought all computers had port 80 open to use web access. I'm not clear with this part.
No - ports are a way *in* to a computer not out. You only need ports open on a computer if that computer is to act as a server.
What do I do to differentiate my computer which is not a webserver with a computer that is a webserver on my router.
Just forward the port. Say a client machine requests port 80 on your IP:
client --> [SOME INTERNET COMPUTERS] --> your router (this is your IP) --> your server (forwarded)
Got it?