Nat Problem? setup problem?

[David Smith]

Goal: Use a linux box as my gateway/firewall, and Host several of my
small web sites with IMAP mail (I'm running Ubuntu 7.04 desktop)

Physical Setup:
I have a speedstream 4200 DSL modem that plugs into eth0 on the linux
box. eth1 connects the linux box to my router and all the other
computers on the network connect to the router. I have
linux.mydomain.com pointing to my IP address. I enabled nat forwarding
on the DSL modem and entered the IP address of my ubuntu box. I
installed apache2 on the linux box.

The Problem:
>From a computer outside the network I see the apache2 default page.
(using the domain name or IP)
>From inside the network with a local IP address (both the eth0 and eth1
IP) I see the apache2 default page.

>From inside the network I can surf no problem till... 

I enter the domain name or my internet IP address...

Then I get the DSL modem login page.

Anyone know where I should be looking to fix this problem?

ps: I'm still a Linux newbie