I have a simple problem that I cannot solve, so I turn to you guys. Your troubleshooting advice will be glorified for eternity.
What I would like to accomplish: Properly configure a RADIUS server to work with my AP.

http://www.marlwifi.org.nz/projects/basic-mt-hotspot

Here is the tutorial I followed to configure RouterOS. My topology closely resembles the one in the picture, but I am also using a WRT54G/DD-WRTv24 AP in between the wireless clients and the RouterOS box.

The Problem: When one wireless clients authenticates, they all do. The UserManager gets the same IP address for all wireless clients connecting to the AP,(WRT54G) which is the AP's WAN IP.

If this isn't enough info I can add more.

sounds like you are running nat on you ap. You should see if you can change it to bridge your wireless and wired interfaces.

woo-hoo! It worked, I am so glad. Thanks for pulling me through this one!