You did the portforward.com thing, right? If you did, go to the Command Prompt, as you can see here.

Then, type in "ipconfig" without the quotients. When you type that in, you'll see this. Note that you have to type in the Default Gateway in your internet brower's URL bar.

You will get into a system, and bam. Then take the steps from portforward.com.
First, you have to find your your Internet's modem model, and then select the application you want to portforward on. Once you get there, there will be many instructions on how to portforward. If you have a 2Wire model, the system would look like this.

Now, follow the directions portforward.com gave you, and you're done.