after searching the forums for solution, i upgraded the router with the new 5.02 firmware and my airport extreme card is at version 3.2. Ii could see the router from my powerbook but i coudn't get any internet connection. When i checked back the network setting, it gave me the 169.25.***.** address. I even tried using manual ip address and i still couldn't get any internet connection.
However when i tried it with the old airport card, it worked. So the problem must be the Airport Extreme Card and router.
What could be wrong? anyone with the successful connection, please help.