Here are a couple of other links that might be of interest.

CMX offers a commercial TCP/IP program for the 8051 called MicroNet that supports Ethernet connectivity. See the following link.
http://www.cmx.com/micronet.htm

CMX and iP Solutions have this working on a Triscend E5-based board called iKit2000. The E5 contains an embedded accelerated 8052 microcontroller.

There is an application note that describes how to connect the E5 to the Cirrus Logic CS8900A 10Base-T Ethernet MAC/PHY chip.
http://www.triscend.com/products/an30.pdf

The complete reference design is available via the following link.
http://www.triscend.com/products/...tml#refdes