FWIW, I've documented the m0n0wall configuration I recently did for a 3 
port (Soekris 4501) box that provides:

DHCP (cable) internet source
WLAN - ethernet port hooked to an AP
LAN - office LAN firewalled off from WLAN

The WLAN network has captive portal enabled, with a 'walled garden 
website' and I also turned on Magic Shaper traffic shaping and remote 
syslogging.

You can read it here: http://socalfreenet.org/node/408

Its doesn't include screenshots, but it might be a handy guide for those 
doing something similar. There's also some links there to the network 
config overview and IP scheme and a sample captive portal page.

Comments welcomed of course! Either via this list or on the page directly.

cheers, michael

PS: Per the Creative Commons license on that website, feel free to copy 
the material elsewhere if its useful (or contact me if you want a 
different copyright release).