If you already have Buffalo WHR-G54S Wireless router I think this tutorial will be helpful for you, for correct configure your home or office wireless network.
In this Tutorial I will show you Network Setup for Buffalo WHR-G54S.
After login to administrative panel of your router, go to Advanced at the top of the home page, next Network Setup and Route Info.
Here, be pressing Edit Routing Information you can edit Routering Settings.
In NAT section in Buffalo Administrative Panel you can edit Turn On DMZ for an IP Address from your LAN. This mean, that everything which is sended to any port for External (WAN) IP Address of the router will be forwarded to this IP Address from your LAN on the same port. By pressing Edit NAT Table button you can set port forwarding for and external to internal (and vice versa) IP Addresses.
Here you can add new rule for NAT Table of port forwarding. Just give name for group, set external (WAN) side IP Address, select Protocol, Internal (LAN Side) IP Address and external (WAN) and internal (LAN) Ports.
Also can edit, delete, pause or stop existing rules in the table.
In IP Filter section you can set Administrative (Add/Delete Basic Rules button) and IP Filter Rules (Configure IP Filter button).
Intrusion Detector is useful if you want to protect and to be notified for any guest which trying to connect to your Buffalo Wireless Router.
If this is happened you can by informed by email address, by pop-up notification with special program installed on your PC of just to be logged in the time.
In the last section you can set UPnP (Universal Plug and Play). This is good if was used more PPPoE connections and some application which supports UPnP.