A few years ago I took an EE class on microcontrollers. We focused on the Atmel AVR family, specifically the AT90S8515 chip. For my final project I designed and built a device which connected to a standard 10-base-T Ethernet network and spoke IP with other hosts on the network.
The system I built uses an NE2000-compatible ISA Ethernet card as the transceiver, and the software implements a basic UDP messaging system. It is a fairly primitive design, but it gets the job done. And for me it was a good vehicle for learning about the ISA bus and microcontroller programming in general.
For hobbyists and experimenters who may be interested, here is the report, with schematics, sourcecode, and even full-color photos: dclausen_ee281_writeup.pdf