DMZ is only possible on the Technicolor 582n BEBox due to the way the BE network is Ethernet based not PPP based.
Generally DMZ is a bad and messy way around correct port forwarding. Everything you require should be possible with a standard port forward.
Adding port forwarding without the horrible web based interface
drsox of the BE Usergroup created a program to make port forwarding on the BEBox simpler and closer to the easy experience of port forwarding on a Linksys. The application cannot edit or delete existing port forwardings on the router, but can add, edit and delete port forwards created using the program itself.
Some users have found that ports they forward via the web interface don't seem to work as planned or don't accept connections. This software seem to fix the problem.
Adding a port forward manually in telnet
If you want to do similar to the above program but by yourself direct in telnet then here are the commands it uses.. (Obviously, don't run the "disable" command unless you want to turn off the port forward you just added.)
:service host add name=BBA1 mode=server :service host rule add name=BBA1 protocol=tcp portrange=6667-7000 :service host assign name=BBA1 host=192.168.1.25 :service host disable name=BBA1 :service host list name=BBA1
Fixing port forwarding
IMPORTANT: This is no longer required for firmwares 7r82y1 (2009-08-03) and above. BE have moved the FTP and HTTPS ports so they no longer conflict with port forwarding.
To enable you to forward HTTPS (port 443) and FTP (port 21) on the 585v7.
telnet 192.168.1.254 Administrator password service system ifdelete name=FTP group=wan service system ifdelete name=HTTPs group=wan saveall exit
You may also want to enable nat loopback to allow your own computers to "loop back" to your forwarded ports:
ip config natloopback=enabled saveall exit