I gave up. I wanted to get a Cable modem (2mbit up and down!) but they are still a long way from making it available at my place so with the help of a friend who works at my telephone provider I will have DSL on the 15th of next month (instead of the 14 weeks waiting period).
The only problem I saw was that my Wireless LAN Gateway can’t really do DSL so I thought I’d need to use my laptop, which has a broken screen anyway, as a server.
When I got the DSL Modem from Net-Cologne (the telephone company) today it included a special user guide done by Net-Cologne themselves. The ADSL modem itself didn’t include any documentation. How weird. Then I wondered. They only want you to connect one PC to the modem, everything else would be against their rules. But hey, who cares for rules. I started looking and found the documentation.
A wonderful device. I can access it via telnet and a browser, set up the DSL config, username and password, if it should stay connected or cut the connection after a given time, DNS forwarding, DHCP if I want and even a simple firewall based on IP addresses that are allowed to connect. Who would have thought that they give me such wonderful hardware for free 
All my worries are settled now and everything will work just fine. When I told my friend he was more than a bit surprised what the device can do. He’s not that technical but wouldn’t have thought that Net-Cologne does something like that anyway.
The only problem I still see is if the device is possibly configured to not give access to the management console. But I will see about that later.