Setting up static IP addresses

hi,
i have 20 computer (installed windows xp) in my office connected to router and I am trying to set up a static IP in order to do port forwarding.so my question is How to set up a static IP address on a Windows XP computer.

Now click on the properties button in the Internet Protocol (TCP/IP) item.

A default configuration will have both Obtain an IP address automatically, and Obtain DNS server address automatically selected.Click on Use the following IP address: and enter the IP address, subnet mask, and default gateway information that your ISP should have given you. (If they did not give you all three, ask them.)

In most cases they will also give you IP addresses for the DNS servers you should use. Click on Use the following DNS server addresses and enter that information as well.That's it. Once you "OK" your way out of those configuration dialogs, your computer should now respond to its assigned IP address.

If you're behind a router, things get a little more complicated.

The first thing to realize is that the static IP address should probably be assigned to the router. That will require configuring the router, much like we configured your server above. Exactly how will vary from router to router, but the principals are the same: you'll configure the router to not get an IP address dynamically, but instead you'll enter the IP, gateway, subnet, and possibly DNS information by hand, using whatever approach your router uses for configuration.

If you want to set up a static IP for your computer using a router. You must find out it's DHCP range and what the IP is of your router. You then want to select an IP out of it's range, to prevent any IP conflicts in the future if you have multiple computers connecting to this router. Your Default Gateway and DNS will be the IP address of your router, as most routers have an internal DNS server or just rerouters DNS requests to their assigned DNS servers from your ISP.
Leave your router set up to whatever it was set up to use weither it was DHCP, Static, PPPoE or any other setting. You do not want to change your router, having your computer set up staticly is enough for your application.
You got that message about your LAN IP being the same as your WAN IP because the WAN IP connects you to the rest of the internet and it got it's IP address from your ISP. You cannot have IPs the same on both ends of a router, that is why it would not allow you to do this.

WAN (Wide Area Network) IP connects your network (LAN) to the rest of the internet.
LAN (Local Area Network) IP connects all your computers in your local network together.

Click on the Start Button and then choose Run. The Run window should open.

Type cmd in the Run box and click OK. A new black window should open up with a prompt.

At the prompt, type ipconfig/all and click Enter. You should now see lots of information related to your IP. Some of this information you will need later - either print the screen or copy down the info for the following fields; IP address, Default Gateway, Subnet Mask and Name Servers (Name Servers are also called DNS Servers). Once all the information has been copied or printed, exit this window.

Click Start and then Control Panel, then select Network Connections. Once the Network Connections window opens, you should see your network connection labeled. Many networks and computers have more than one network connection. Choose the network connection that you use to connect to the internet. Once this network connection is selected, right click and choose properties.
Hint: If you are having difficulties finding the network connection that is used to connect to the internet, one way to make your search easier is to disable one connection at a time and then test using your browser if your internet still works. If your internet no longer works, then the network connection you disabled is the one that you use to connect to the internet.

In the Properties window, select the General tab and then click on Internet Protocol (TCP/IP). Once this is selected click on the Properties button.

On this screen, choose the following radio button: Use the Following IP Address and then you will fill in the following information regarding:
IP Address
Subnet Mask
Default Gateway

There will also be two radio buttons. Choose the radio Button: Use the Following DNS Server Address. There are two more fields to fill in, they are:
Preferred DNS Server
Alternate DNS Address

Once this information has been added, click OK. A static IP address has been set for Windows.