Ok, I took it the easy (or was this one called the "hard") way. I just took the Arduino Ethernet library and rewrote it for the W5200 commands.
Just download T3Libs to your Arduino/Sketches/Libraries folder and have fun.
I added a few examples a few minutes ago. It's not polished but works. The inferface is still compatible with the official Arduino Ethernet Library, the DHCP client code worked out of the box as soon as I got basic commands up and running.
I've not yet decided if I'll invest more time into it or just wait for an official release by someone with better coding skills and more time. Maybe there already is something somewhere but at least it was an interesting *project*.
