> If a dmz server use the first firewall as default gateway the LAN
> clients that have the second firewall as default gateway cannot connects.
> 
>            +-> ADSL1 <-> m0n01 <-+
>            |                |    |
> Internet <-|               DMZ  LAN
>            |                |    |
>            +-> ADSL2 <-> m0n02 <-+

if m0n01 and m0n02 are connected via LAN, you can add a static routing
to DMZ-IPs via m0n01 if you want to connect clients with m0n02 as
gateway to DMZ.

see http://m0n0.ch/wall/docbook/config-system.html if you dont know
how to handle it...