And for reference, problems should be posted in the Emergency forum, but its not a big problem, just seems to be popping up more in here then it used to. Just an observation, this is not criticism in anyway.
Might be a couple of things to try. (For one, Apple's Tech support at 1-800-263-3394 might be of assistance)
Are you connecting to high speed cable or DSL? If its cable, I have seen the problem several times where cable internet providers use cable modems and they "lock" into a specific computer. The reason for this is because each computer's internet hard has a unique hardware identity or address called a MAC address. (Nothing to do with Macs)
Sometimes, you have to get the cable modem to "let go" of that particular address and accept the new one. (In this case, the Airport base station has its own ethernet port, thus its own unique MAC address).
Sometimes a call to your cable ISP will rememedy this as they can release the address.
This is probably as clear as mud and most likely confusing you more.
The first step is to try to connect to your internet provider directly to your new AlBook to make sure you can get a good connection with that. If not, call your ISP and get them to help.
Once you have a good connection on your AlBook, plug in the AirPort to your internet connection and the run the AirPort Setup Assistant from your AlBook which is in your Applicaitons forlder --> Utilities
If that doesn't work then, try giving the Apple number a call. (Or maybe another ehMac member will be able to explain it better)