There is an Ad placed on the top of that site for 'PConfig'.. it is just that an ad for a program that automatically forwards ports. This is not what we are asking you to get, its not free and its annoying they way they have it placed on the site but they do offer all these guides for free and they have to make a living somehow....
however.. if you click the link near the left top that says Port Forwarding (also on this line at the top you see Port Triggering, Firewalling, wireless networking etc.. just to make sure your clicking the right spot) you will see many routers/modems listed and all you need to do is find your brand, then model and click on it. You will then see a list of programs you may want to forward, find WinMX on the list and click this. Now you will see a FREE guide with pictures on how to manually forward your ports.
Id get you a direct link but am unsure what model and brand your looking for.