help connecting atmega32 micro-controller to LAN
There are quite a few diagrams and tutorials on the web that will help you achieve this.  I think the obvious choice would be to use SPI to interface to either a W5100 or ENC28J60 based board since your chip supports that.

You might be able to get smaller boards that would be better suited to your needs, but before you buy you should check that there is a library that will suit your needs.