Well, first you're going to need to get to your router's configuration page. Then, you're going to have to find DMZ settings (if your router supports it, it probably will). On my router, all I do is type in the internal IP address of the computer I want DMZ'ed, and hit "save settings."
On your network, each one of your computers has an internal IP address, 192.168.0.something. They're usually assigned randomly by your router upon connecting (via DHCP, you're going to have to configure a static IP address for your server once you get it set up). These internal addresses are how your router identifies each separate computer on your network. Other people can't access your computers through these addresses, because it's only your local network. As far as the outside world sees you, you're just your
external IP address, no matter what PC on your network you're using.
In a nutshell, your router takes your external IP address, and splits it across as many computers as it supports on your network. This is all fine and good, until you want to do something that requires special ports. The computer on your network sends the request to your router, which sends it off to wherever on the Internet. It gets a response back, but where on the network is it supposed to go? The router doesn't know which computer to
forward the traffic from this
port to (hence, port forwarding)! So, what you're doing by port forwarding is telling the router, "Hey, when traffic comes in from port
x, I want you to deliver it to the computer located at
192.168.0.x!"
*disembodied voice* Now you know! That's DD's bit on basic general networking.
So, find your computer's internal IP address. I think on Windows it shows it when you look at your network connection's status (right click on the icon of the two computers on your system tray). That's the IP address you tell your router you want the ports forwarded to, or DMZ'ed.
Have I referred you to
this website yet? It's a good, helpful resource, and it has everything you need to get you up and running. My fingers are gonna start cramping if I have to type up another post like this. D;