Thanks for the informative response!
Ok. So set up my WAN to come in on my 2500 through the RJ45 'aux' port. I understand some of what your saying with the commands to do this. I'll see if I can track down the commands for DHCP. Alternativley, is it possible to simply connect it to another router through the aux port before going to the WAN? Such as a d-link or linksys basic soho router that automatically assigns DHCP? Or would it be better to figure out how to do it with the 2500?

Two more questions:
The 'AUI' DB12 interface I can use for my LAN, correct? That is to say, plug it into a hub or switch and I'm set. First, I believe I'll need a transceiver to convert it to RJ45 and then I'm good.
The DB60 serial on the 2500 *which I originally thought I had to connect to the WAN with) I can simply use to connect to my other cisco router, correct?