Robert,
I used my Dell 3100cn with a Linksys wireless broadband router for nearly three years. The Dell is indeed Mac compatible. It's just that Dell has absolutely no support for the Mac.
What seems to be occuring is that the AEBS is not communicating with the Dell and, therefore, the IP address is not being set by the AEBS DHCP server. (As I state above, the Dell still shows the address set by the Linksys.)
As for my AEBS, I had to power it down several times and reset it several times before everything worked right. The key was setting the Channel to 11 manually. Until then, I could never connect to the Internet. After setting it manually on my Ethernet connected Mac, I then couldn't get the wireless signal recognized by the Airport enabled Macs. Finally, I reset the AEBS one last time and reconfigured everything, including manually selecting the channel, and the wireless signal was restored.
I'm sure I created a lot of my own problems with the AEBS but it wasn't completely clear-cut.
Now, if I can only get my Dell printer going!
Michael