I don't remember the specific requirements, but I believe the CMX MicroNet software for the 8051 does the PPP protocol in about 3K, but there is additional overhead if you are using TCP/IP or UDP as your protocol.

A company called iP Solutions and CMX have built a demonstration web-server over Ethernet using a Triscend E5-based iKit2000 board. There are more links at
http://www.8052.com/users/skn...rnet.phtml

In specific, take a look at page 11 of the following link. As part of the CMX demo, they show the ROM requirements for various components.
http://www.triscend.com/products/...0_demo.pdf