I have browsed through the forums but i can't seem to find a solution.
I've found the External NAT limitation too but i still can't make it
work. I'm a total newbie to NAT and such and i only rely on linksys
firmware to do port forwarding for me. Linksys works but i need to add
a capture portal for my new wireless network by adding a m0n0wall PC.

I can't access my website (host internally through m0n0wall.)

I.  My original setup (working)

WAN --- AP/Router ---- Router
              |                       |
            WLAN    WEBSERVER and wired PCs

AP is has local 192.168.100.1 serving DHCP for WLAN

Router is connected to AP via Internet Port and has static
192.168.100.2 and local 192.168.101.1. This router is serving DHCP for
Wired PCs

Webserver is static 192.168.101.22 whose gateway is setup to
192.168.101.1. DNS is set through WAN (ISPs) DNS.

DDNS is through Zoneedit with multiple hostnames (e.g.
mynet1.mydomain.com, mynet2.mydomain.com).

The Webserver hosts 2 websites through IIS with hostnames mynet1 and
mynet2 .mydomain.com

At Linksys AP, Port 80 is forwarded to Port 80 of 192.168.100.2
At Router, Port 80 is forwarded to Port 80 of 192.168.101.22




II.  Intended setup with m0n0wall (to add capture portal for WLAN with
the previous features)

Objective: WLAN to get affected by Capture portal while having an
accessible web server through LAN and WAN.

WAN --- m0n0wall --- AP --- Router
                  |             |             |
    Capture Portal     WLAN     Webserver and Wired LAN

How will I go about this setup? Is this a right network setup for my
needs? If not, what will work?

How will i setup m0n0wall to do the same tasks as the what the port
forwarding of Linksys AP/Router does?

I spent 3PM - 2AM of my time making it work but i failed. =(

Thank for any help you guys can extend.