[Satcomer]

Well this first thing you have to do is decided if this will being doing the NAT or is sitting behind a NAT. I say this because you will have problems if the wireless sits behind a wired router. I do it this way and using /Applications/Utilities/AirPort Utility and setting the Connection settings (in the Internet tab) and turn "Connection Sharing" off "Bridge Mode". This way my wired router is doing the NAT and the Airport Extreme is just broadcasting IPs for it (for my wireless devices).

So if you connect to it launch /Applications/Utilities/AirPort Utility and set the setting there, only is it sits behind a main router. Plus since it is an older Airport Extreme ask yourself what kind of wireless & wireless security (b or g) you can use.

Note: If this Extreme is less than three years old make sure you are using at least CAT5E cable connecting it up.