I'm doing something like your project with a modern devices BBB and I constructed a piggyback proto-board that the wiznet board mounts onto.
I have been playing with some code that I have on the net at wb2ibo.myvnc.com:5050 Feel free to toggle the outputs, it is interfaced to LED's. I am wiring up a single board solution that will have LED's and a small prototyping area along with headers to interface with the outside world.
I would like to make several of these boards and am looking into even expanding it to a larger AVR chip as well.
I need to clean up my code and will post it when I get that done.