micro arduino and w5100
While it would have been nice to see your research rather then having to spend some time finding this information myself, I did find this http://www.instructables.com/id/Add-Ethernet-to-any-Arduino-project-for-less-than-/ from what I can see this should be compatible to any arduino as long as it has 3 volt pin and 4 i/o pins. While the arduino micro doesn't have a 3v3 pin, as far as I know, that shouldn't be an issue as long as you can drop the voltage from the 5 volt pin, this module should work for you.